Pasteurization, development and storage of sous vide rendang (spicy beef stew): Product and...

Pasteurization, development and storage of sous vide rendang(spicy beef stew)

Stella Marie Colima Galimpin-Johan,* Russly Abdul Rahman,* Bakar Jamilah,*Yaakob Bin Che Man* and Gulam Rusul†

*Department of Food Technology, Faculty of Food Science and Technology, University Putra Malaysia,Serdang, 43400 Selangor D.E., Malaysia; †School of Industrial Technology, Universiti Sains Malaysia,11800 USM Penang, Malaysia

Correspondence:S. M. C. Galimpin-Johan,Department of FoodTechnology, Facultyof Food Science andTechnology, UniversityPutra Malaysia, Serdang,43400 Selangor D.E.,Malaysia Tel: +60 389468377; Fax: + 60 389423552; E-mail:[email protected]

Keywords:Sous vide, pasteurization,beef

Abstract

This study aims to develop product and processing parameters of sous viderendang and to examine its quality changes during storage. Sous vide rendangmay be pasteurized for 443 min at 75°C and for 88 min at 85°C using fastheating to meet the Pv90 = 10-min guideline for pasteurization. Process-meat-formulation combinations of sous vide rendang indicated that processingat 85°C/2 h, the use of rump and formulation 1 (F1) produced better sensoryproperties. Water activity (Aw), aside from pasteurization, is a possible con-trolling factor for sous vide (SV) rendang but not pH. Conventionally cooked(CC) rendang stored at 2°C and sous vide rendang pasteurized at 70°C/100 min (SS70) and at 85°C/2 h (SS85) stored at 2 and 10°C can last for 35days using microbiological count as its storage indicator. Applications ofguidelines by the UK Food Standards Agency would mean that the maximumshelf life allowable for CC and SS70 will only be 10 days compared to SS85,which is 40 days.

Introduction

Sous vide (Cuisine en Papillote Sous Vide) is aninterrupted catering system in which raw or par-cooked food is sealed into a vacuumized, lami-nated plastic pouch or container, heat treatedby controlled cooking, rapidly cooled, held atrefrigerated temperatures and then reheated forservice after a period of chilled storage (Baird1990; Schellekens 1996; Creed 2000). Sous vide(SV) is also defined as a specialized process ofreduced oxygen packaging (ROP) for partiallycooked ingredients alone or combined with rawfoods that require refrigeration or frozen storageuntil the package is thoroughly heated immedi-ately before service (USFDA 2005). Generalprocessing steps involved in SV are preparation

of raw materials, vacuum packaging, pas-teurization, chilling/cooling, chilled storage andreheating (Church & Parsons 1993; USFDA2005).

The SV method produces food with a betterflavour, colour, texture and nutrient retentionthan conventionally cooked foods. Anecdotalevidence compiled by Creed (1995) for thesensory and nutritional quality of SV-processedfoods describes the process in a positive manneras a better alternative compared with conven-tional or traditional methods. The use of vacuumpackaging in SV processing prevents degradationand oxidation in food products and reduction ofproduct shrinkage by preventing water loss(USFDA 2005); thus, sensory properties of thefood are retained and enhanced.

Original article

© 2007, The Authors

Journal compilation © 2007, Blackwell Publishing Journal of Foodservice, 18, pp. 251–263

251

mailto:[email protected]

SV food products only require prior reheatingbefore serving; thus, one of its obvious advan-tages is its convenience. The key to a successfulentry into the global food industry, valued at €3.2trillion, is to understand the mega trends thatinfluence buying behaviour, the chief of which isconvenience. Time-saving products, such as pre-pared meals in Europe and in the USA, are fore-casted to double in 10 years, exceeding US$50billion by 2009, which is up from US$29 billionin 1999 (Anon 2005).

Malaysia’s demand for convenience food is alsogrowing, a trend that is identical with the globalmarket. Fresh produce is still preferred, but pur-chase of frozen and chilled processed food hasincreased with economic growth. Increased own-ership of microwave ovens and refrigeratorshas led to the increase in consumption of pre-prepared convenience meals and frozen foodproducts, while growing affluence and the in-crease of women in the workforce have contrib-uted to the frequency of dining out (Austrade2007).

More products that are convenient and easy toprepare need to be developed in order to meetthe growing market demand for convenience inMalaysia. A feasible alternative is to process tra-ditional food products presented in a convenientmanner. Rendang or spicy beef stew is a dishtraditionally served during weddings and specialoccasions in Malaysia. Because of its complexityin preparation, cooking rendang is time consum-ing and laborious; thus, it is an excellent choicefor SV processing. SV is envisioned as one of thetechniques to support the increasing growth of itsfoodservice sector. Malaysia has a large foodretail and beverage sector, worth US$12.6 billionin 2003, wherein the foodservice sector is valuedat US$3.813 million and is expected to grow5–15% in the next 3 years (USDA ForeignAgricultural Service 2004).

The growth of spore-forming bacteria (SFB) is asafety concern associated with the production ofSV products. Carlin et al. (2000) mentioned thatthe main hazards identified in cooked, chilled veg-etables were Bacillus cereus and psychrotrophic,non-proteolytic Clostridium botulinum (GroupII), which was based primarily in their ability togrow at 3°C for C. botulinum and at 4°C for B.cereus. According to Betts & Gaze (1995), there

were several reasons for the survival and growthof the psychrotrophic strains of C. botulinum inSV products. First, vacuum packaging creates ananaerobic atmosphere that selects for facultativeand anaerobic microorganisms; second, minimalheat treatment, which targets the elimination ofvegetative pathogens at 70°C for 2 min, will nothave any effect on bacterial spores that may growif conditions are favourable; lastly, chilling duringstorage selects for psychrotrophic organisms –therefore, the absence of competitive microfloraafter minimal heat treatment allows proliferationof SFB.

Rhodehamel (1992) also mentioned that SVproducts are generally formulated on the basis ofdesired organoleptic qualities and not on safetyconsiderations. In addition, SV products receiveminimal thermal processes and are therefore notshelf stable. Although vacuum packaging mayextend shelf life by inhibiting aerobic spoilagemicroorganisms, it may produce an environmentsuitable for anaerobic microorganisms. There-fore, adequate refrigeration must be maintainedat all times to prevent outgrowth of C. botulinumand the subsequent production of toxin.

The UK Food Standards Agency (UKFSA 2004)specified five controlling factors to limit thegrowth of food poisoning microorganisms thatwere identified as the non-proteolytic, psy-chrotrophic C. botulinum. These are heattreatment, acidity of the food, salt content,water activity and a combination of factors.For vacuum-packed/modified-atmosphere-packedchilled foods with a shelf life of greater than 10days and up to 40 days at chill temperatures of�8°C, the minimum heat treatment requirementis that the slowest heating point (SHP) of the foodshould be held at 90°C for 10 min (Pv90 = 10 min)or equivalent (85°C for 36 min, 80°C for129 min, 75°C for 464 min). A pH of 5.0 orbelow throughout the food stored at �8°C issufficient to inhibit the growth of psychrotrophicC. botulinum.

At 3.5% level of salt throughout, the aqueousphase of a food stored at chill temperatures of�8°C is also sufficient to inhibit the growth ofpsychrotrophic C. botulinum. Water activity (Aw)of 0.97 or lower should be achieved through-out the food stored at chill temperatures of�8°C to inhibit the growth of psychrotrophic

252 Product and processing parameters of spicy beef stew S. M. C. Galimpin-Johan et al.



C. botulinum. Combinations of a lower level ofspecific controlling factors described previouslymay be able to prevent growth or to inhibit thegrowth of psychrotrophic C. botulinum. For longshelf life of foods (>40 days) stored at chill tem-peratures of �8°C, it is suggested that, in additionto a heat treatment of 90°C for 10 min (or equiva-lent such as 85°C for 36 min, 80°C for 129 minand 75°C for 464 min), challenge testing be con-ducted to establish the maximum shelf life.

Chilling is one of the main hurdles associatedwith the production of vacuum-packed chilledproducts. Recently, a revision has been proposedto the Advisory Committee on the Microbiologi-cal Safety of Food that short shelf life foodswithout any controlling factors may be stored at�8°C with a shelf life of �10 days, rather thanstorage at �5°C and a shelf life of �10 days orstorage at �5–8°C and a shelf life of �5 days.The proposed change in storage was based onepidemiological evidence with regard to food-borne botulism wherein no incidence of food-borne illness occurred when food was properlystored (Peck et al. 2006). Conversely, USFDA(2005) recommended that foods in ROP that haveonly refrigeration as a barrier to C. botulinummust be refrigerated to 5°C or below and markedwith a use-by date within either the manufactur-er’s use-by date or 14 days after preparationat retail or whichever comes first. Moreover,employees must undergo training on ROP, andthe statement ‘must be kept refrigerated at 5°C’must be indicated in the food label.

Previous studies (Ollinger-Snyder et al. 1995;Armstrong & McIlveen 2000; Jang & Lee 2005;Jang et al. 2006; Paik et al. 2006) have shownthat the microbiological and sensory aspects ofSV products are critical to their safety and accept-ability. Microbiological quality of ground porkpatties, using SV with or without rice hulls, wereprocessed up to an internal temperature of 62and 76°C and stored chilled at �1°C for 1, 2 and3 weeks. Lower temperature was selected toproduce a product with an internal temperaturebelow that specified by the Food and DrugAdministration for cooked pork, whereas thehigher temperature was selected to produce aproduct with an internal temperature within theSV guidelines for cooked pork. SV ground porkpatties (with or without rice hulls) were micro-

biologically acceptable when the products wereheated to an internal temperature of 76°C andstored for 3 weeks. Upon cooking at a lowertemperature (62°C), unacceptable levels ofaerobic plate count were observed during the 3weeks of storage (Ollinger-Snyder et al. 1995).

Shelf-life studies were conducted on minimallyprocessed SV spaghetti and meat sauce productssubjected to a heat processing at 65 and 75°C,equivalent to a 5 and 13 D reduction of Strepto-coccus faecium, and subsequently stored at refrig-eration (5°C) or under mild temperature abuseconditions (15°C). Products stored at 5°C had ashelf life of �35 days irrespective of the process-ing treatment. However, for products stored at15°C, packages were visibly swollen after 15–21days, depending on the severity of the heat pro-cessing treatment. Initial spoilage microorganismsconsisted predominantly of Bacillus species;however, after 7–12 days at 15°C, lactic acid bac-teria accounted for almost all of the spoilagemicroorganisms (Simpson et al. 1998).

Bolognaise meat sauce was vacuum packed andprocessed at 70°C for 900 min, chilled to below3°C in less than 2 h using iced water and thenstored in air for 40 days. The products werereheated at 75°C for 15 min before serving topanelists. Sensory evaluation was conducted on 0,10, 20, 30 and 40 days. Appearance seemed tohave the greatest impact on products. Consumershad no preference for the day 0 products, whichindicated that an SV bolognaise meat sauce couldbe successfully stored for 40 days at 0–3°C and beof acceptable sensory quality to consumers (Arm-strong & McIlveen 2000).

SV processing of Korean seasoned beef or jang-zorim was developed, which has better sensoryquality and storage stability compared with con-ventionally processed jangzorim. The sensoryquality-based shelf life of the SV-processedproduct was around 12 days at 3 and 10°C, whichwas significantly longer than the conventionalproduct. The SV packaging was effective in pro-tecting the product from microbial, physical andsensory quality degradation (Jang & Lee 2005).The combined addition of vinegar and sake may bea possible alternative as it offers a significantlyimproved microbial stability and an insignificantminimal loss of organoleptic quality with storage(Jang et al. 2006). SV-processed packages, with or

253Product and processing parameters of spicy beef stew S. M. C. Galimpin-Johan et al.



without nisin (100 or 500 IU), were stored at 4 and25°C. All packages stored at 4°C exhibited nomajor changes during 60 days of storage. In thecase of 25°C storage, the number of mesophilicmicroorganisms increased markedly, but withnisin application, no observed increase of saidmicroorganisms was observed. Psychrotrophicmicroorganisms, anaerobic microorganisms andB. cereus cells showed similar trends, althoughClostridium perfringens was not detected in thesamples (Paik et al. 2006).

This study aims to develop product and pro-cessing parameters of sous vide rendang (spicybeef stew) based on the conventional method ofprocessing and incorporating the heat treatmentrequirement of Pv90 = 10 min and to examine thequality changes that occur during chilled storagefor conventional and SV-processed rendang.

Materials and methods

Sous vide rendang preparation

Frozen beef was purchased from Makro Cheras,Kuala Lumpur, Malaysia, and was then stored inthe laboratory freezer at –18°C until processed.These frozen beef parts were hygienically pro-cessed and packed by Al-Nafee’s Frozen FoodExports Pvt. Ltd., Goa Meat Complex, Usgaon,Goa, India, and are purchased by the foodservicesector. All other fresh materials were bought at thewholesale market with the exception of packedcoconut milk (M S brand, Selangor, Malaysia),which was purchased from the supermarket inbulk and used for the whole duration of the study.

Rendang formulation utilized in the study wasadapted from the rendang minangkabau recipe byYew (1999), which originates from Negri Sembi-lan, a federal territory of Malaysia. This formula-tion is composed of beef, coconut, dried chillies,bird chillies, lemongrass, galingale, ginger, tur-meric, shallots, garlic, tamarind skin and kerisik(toasted, grated coconut). Dried chillies refer tolong red chillies of approximately 10-cm long witha mild spicy taste, while bird chillies are usuallygreen, yellow or red, 2- to 3-cm long and are veryspicy. Spiciness of the food is a common trait ofmost of the dishes found in Negri Sembilan.

Rendang is processed conventionally by mari-nating the beef for 15 min with ground ingredi-

ents consisting of chillies, galingale, ginger andturmeric root. Coconut milk is poured into themixture and brought to a slow boil. Lemongrassis added and the mixture simmered over low heat,with frequent stirring. Pan-fried grated coconut(kerisik) is then added and the mixture simmered,with frequent stirring until the meat is tender andthe gravy is thick. In a separate saucepan, oil isheated, and shallots and garlic are browned andadded to rendang. Depending on the manner ofcooking and amount of rendang, cooking timecan range from 2 to 8 h.

Materials were converted into percentage forease of production as shown in Fig. 1. The majorprocessing steps were identified as follows:material preparation, marination, slow cooking,hot filling, vacuum packaging, pasteurization,rapid cooling and chilled storage. Equipmentspecifications are also mentioned in Fig. 1.

Evaluation of pasteurization values

One hundred fifty grams of rendang was vacuumpacked in laminates of nylon/EVA/PE with a 3-mil

1.4% Galingale1.4% Ginger0.7% Turmeric 6.7% Onions 3.4% Garlic 0.8% Dried Chillies 0.4% Bird Chillies 1.7% Lemongrass

MATERIAL PREPARATION (peeling, slicing, grinding)

MARINATION(20 min at room temperature of 25±1oC)33.3 % Beef

(1 in x 1 in x 1in)

SLOW COOKING (CUT = 20 min, 60 min cooking time)

HOT FILLING(8.5 x 6 in laminates of nylon/EVA/PE, 3 mil thickness)

VACUUM PACKAGING (Vacmaster SVP-40, 28.5 mmHg)

PASTEURIZATION(Protech 850 Water Bath, PV90 = 10 min or equivalent)

RAPID COOLING (in ice slurry)

CHILLEDSTORAGE

33.3 % Coconut milk 16.7% Water

Figure 1 Process flow for the preparation and pro-cessing of sous vide rendang (adapted from Yew1999). CUT, come-up time; EVA, ethylene vinylacetate; PE, polyethylene.




thickness and subsequently heated in a Protech830 (Protech Electronic, Malaysia) water bath(Protech Electronic, Selangor, Malaysia) to obtainthe time–temperature history of the product at75, 80, 85 and 90°C using slow and fast heating.Slow heating refers to SV processing, wherein theproduct is pasteurized in a water bath initially atroom temperature (25 � 1°C) and subsequentlyheated until the desired temperature is reached.Fast heating refers to SV processing, wherein theproduct is added after the water bath has reachedthe specified temperature for pasteurization.Thus, come-up time is �45 min for slow heatingand only 2 min for fast heating. Utilizing D- andZ-values of C. botulinum (Betts & Gaze 1995),pasteurization value or Pv was computed usingthe graphical method (Stumbo 1973; Alabastro1987). Two trials were conducted, and the highervalue computed was utilized as the pasteurizationprocess.

In order to obtain a better safety factor withregard to the computation of the eventual pas-teurization process, the SHP of the product wasobtained through a series of experiments involv-ing the length of the probe inserted insidethe vacuum-packed rendang. Three points weretested, namely, 3-, 4- and 6-cm length of the probe(data not shown). Inserting the probe at 4-cmheight provided the SHP for both slow heatingand fast heating. Thus, subsequent experimentswere conducted at 4-cm probe length to obtainthe heat penetration data.

Development of sous vide rendang

A completely randomized design was appliedduring the development of SV rendang using threevariables: formulation, sous vide processing andmeat parts. Two formulations were applied, for-mulation 1 (F1) being the original formulationas outlined in Fig. 1. Ingredients consisting ofonions, garlic, ginger, galingale and turmeric werehalved from the original formulation and werethen represented by formulation 2 (F2). The ratio-nale was to observe whether minimal amounts ofingredients would affect its acceptability uponprocessing with SV. Processing was conducted tomeet the requirement of a 6-D reduction of psy-chrotrophic C. botulinum. From prior experi-ments and computations, two time–temperature

combinations were chosen to represent a low-temperature/long-time process (75°C/8 h) and ahigh-temperature/short-time process (85°C/2 h).Frozen beef rump (m. biceps femoris), topside (m.semimembranosus) and knuckle (m. quadricepsfemoris) were used in the study. The beef partswere chosen primarily because of their availabil-ity and reasonable price, with rump, knuckle andtopside costing RM 5.99, RM 6.00 and RM 6.39respectively (US$1 = RM 3.45).

Storage studies

Beef rump was selected due to its availability,reasonable price and sensory properties. Follow-ing the adapted formulation of rendang, samplesproduced were weighed and packed as men-tioned. Three processing conditions were thenapplied to rendang, namely, conventional cooking(CC), in which samples were packed undervacuum without any pasteurization, SV process-ing at Pv70 = 100 min (SS70) and SV processing at85°C for 2 h (SS85). CC represented a grosslyunder-processed product; SS70 is a requirementset by French regulations for sous vide-processedproducts using Streptococcus faecalis as the refer-ence microorganism (Church & Parsons 1993)for products stored up to 21 days. This is alsoequivalent to Pv90 = 0.1 min, under-processedusing the criteria of UKFSA of Pv90 = 10 min.SS85 was the result of the Pv process computedfrom the preceding experiment and meets thespecified requirement of UKFSA. The sampleswere then stored at 2 and 10°C. Physicochemicaland microbiological analyses were conducted ondays 0, 21 and 35 of storage.

Two storage trials were performed whereinfour packs each of stored rendang were taken outfor each sampling, two packs for physicochemicalanalysis and two packs for microbiologicalanalysis, each pack representing a replicate.

Physicochemical analysis

Exactly 10 g of a sample was weighed andhomogenized with 90 mL of distilled water. ThepH of the sample was measured using a MettlerToledo 320 pH meter (Columbus, OH). Wateractivity was measured by using the Aw meter(Aqualab Model Series 3 TE, Decagon Devices




Inc., Pullman, WA). The rendang sample washomogenized and then filled into a plastic disc,just enough to cover the bottom of the disc. Thedisc was then inserted into the Aw meter, and thedatum was read upon stabilization. Moisturecontent was determined following the Associationof Official Analytical Chemists (AOAC 1990).Exactly 5 g of samples were weighed and dried ina Memmert air oven (UM 500, Schwabach,Germany) at 105°C for 16–24 h, after whichthe sample was cooled in the dessicator andweighed.

Microbiological analysis

Rendang packs were aseptically opened, and 10 gof the sample was weighed into a sterile stoma-cher bag. Then, 90 mL of sterile 0.1% peptonewater (Difco Laboratories, Becton, Dickinson andCompany, Sparks, MD) was poured into the bagand homogenized in a stomacher (Seward Stoma-cher Blender, Model 3500, BLD Inc, Garner, NC)for 2 min at high speed. Aliquots were dilutedusing 0.1% peptone water in 10-fold dilutions,and 0.1 mL was plated out into the specificmedia.

Total mesophilic anaerobic count was platedin anaerobe agar (Merck KGaA, Darmstadt,Germany) and incubated anaerobically using aBBL anaerobic jar at 35°C for 48 h. For the enu-meration of C. perfringens, the homogenate washeated at 75°C for 20 min and plated in tryptosesulfite cycloserine (TSC) agar. The plates wereincubated upright anaerobically for 18–20 h at35°C. Bacillus cereus was plated in polymyxinpyruvate egg yolk mannitol bromothymol blueagar (PEMBA) (Oxoid) medium and incubatedfor 24–48 h at 35°C. The analyses mentionedwere conducted according to procedures of theAmerican Public Health Association (APHA1992).

Chromogenic media (ChromAgar Microbiol-ogy, Paris, France) was used for the analysis ofListeria monocytogenes, Salmonella sp., Staphy-lococcus aureus and total coliform count. Proce-dures for preparation, incubation and detectionwere followed according to their product proto-col. The plates were incubated at 37°C for 24 hand were interpreted as follows: blue, regularwith white halo for typical colonies of L. mono-

cytegenes; mauve for Salmonella sp.; mauve for S.aureus, and red for total coliforms.

Sensory evaluation

Panelists were sourced out from the Master ofScience and Doctor of Philosophy students of theFaculty of Food Science and Technology, Univer-siti Putra Malaysia. All of them had taken at leastone course in sensory evaluation during theirundergraduate course and were familiar with therendang dish, since they consume the dish at anaverage of once per month. Although the panel-ists were familiar with the dish, a preliminarymeeting was set up to familiarize the prospectivepanel with the SV-processed dish and to come upwith some terminologies to describe rendang. Tenpanelists evaluated the samples for flavour (norendang flavour to intense rendang flavour), spici-ness (not spicy to spicy), texture (soft to hard) andacceptability (dislike intensely to like intensely).The attributes were evaluated in a 10-cm linescale with two vertical lines at opposite ends. Thepanelists were instructed to rinse the palate withwater after each sample testing (Meillgaard et al.1999).

Statistical analysis

Data were analyzed through one-way analysis ofvariance and Duncan’s multiple range test usingSAS version 9.1 (SAS Institute Inc., Cary, NC). Tstatistics were also conducted to determine differ-ences in F1 and F2 formulations.

Results and discussion

Pasteurization studies

The advantage of the SV system for processing ofrendang is the incorporation of vacuum packingand pasteurization. Vacuum packaging inhibitsboth aerobic spoilage and oxidative rancidity,which produce off-flavours during chilled storage.Sensory quality is maintained by preventingevaporative losses of water and flavour volatilesduring pasteurization and by the moist conditionsduring the pack, which facilitates transformationof collagen to gelatin during pasteurization,increasing meat tenderness (Church & Parsons




1993). Pasteurization lengthens the shelf lifeof the SV product. Studies showed that SVbolognaise sauce processed at 70°C for 900 minwas still acceptable upon storage at 3°C for 40days (Armstrong & McIlveen 2000). SV Koreanseasoned beef was pasteurized at 97°C for 11 minwith a sensory quality-based shelf life of around12 days at 3 and 10°C (Jang & Lee 2005).

Figure 2 is a graphical illustration of the lethal-ity curve at 75, 80, 85 and 90°C. Lethality curvesshowed that fast heating increased more rapidlyat SHP compared with slow heating. This obser-vation was more evident at the higher tem-peratures of 85 and 90°C compared with 75 and80°C. Furthermore, the difference between slowand fast heating in terms of the pasteurization

process was clearly distinguishable at 90°C com-pared to the lower temperatures. Because of theseinferences, fast heating was selected for thesubsequent heating regimen of the study.

Table 1 shows the pasteurization processes inminutes, computed using the graphical method(Stumbo 1973; Alabastro 1987). As defined byGhazala et al. (1995), reference pasteurizationvalue, or Pv, is the product of the requirednumber of decimal reduction (n) of a targetmicroorganism and its decimal reduction time(D) at a reference temperature. To obtain thevalues of Pv of the product, D-values of the ref-erence microorganism were gathered from litera-ture and multiplied by the order-of-the-processfactor of 6. Betts & Gaze (1995) stated the heat

Figure 2 Lethality curves of sousvide rendang pasteurized atdifferent temperatures. Water bathtemperatures at (A) 75, (B) 80,(C) 85, (D) 90°C. S1 and S2 –slow heating, F1 and F2 – fastheating.

A

-0.20

0.00

0.20

0.40

0.60

0.80

1.00

0 100 200 300 400 500 600 700

minutes

leth

ali

ty

75S1 75S2 75F1 75F2

B

-0.20

0.00

0.20

0.40

0.60

0.80

1.00

0 50 100 150 200 250

minutes

leth

ali

ty

80S1 80S2 80F1 80F2

C

-0.20

0.00

0.20

0.40

0.60

0.80

1.00

0 20 40 60 80 100 120

minutes

leth

ali

ty

85S1 85S2 85F1 85F2

D

-0.20

0.00

0.20

0.40

0.60

0.80

1.00

0 20 40 60 80 1

minutes

leth

ali

ty

00

90S1 90S2 90F1 90F2




resistance of psychrotrophic C. botulinum in codas D-value of 53.90 min (75°C), 18.30 (80°C),4.00 (85°C) and 1.1 (90°C) at Z-value of 8.64.The authors also mentioned that a safety marginwas incorporated to the recommendation ofPv90 = 10 min to allow for variation in heatresistance between strains and in different foodproducts.

For C. botulinum to be inhibited at the required6 log reduction, SV rendang must be heated for478 or 443 min at 75°C and for 96 and 88 min at85°C using slow- and fast-heating systems respec-tively. Note that the computation for C. botuli-num is in accordance with UKFSA (2004) andPeck et al. (2006). UKFSA has suggested that forthe storage of vacuum-packed chilled products(such as SV) at �8°C for more than 10 days, oneor more of the following specific controllingfactors must be applied, such as a minimum ofheat treatment of 90°C for 10 min, pH of 5.0 orless throughout the food, a minimum salt level of3.5% (aqueous), Aw � 0.97°C throughout thefood and a combination of heat and preservationfactors that have been shown to consistentlyprevent growth and toxin production of C. botu-linum. Peck et al. (2006) have recommended thatshort shelf life foods without any controllingfactors may be stored at �8°C with a shelf life of�10 days.

Results obtained from this phase were then uti-lized in the development studies, namely, the twopasteurization combinations of 75°C/8 h and85°C/2 h.

Development studies

Significant difference (P < 0.05) in terms of pHwas observed for all SV rendang combinations forpasteurization–meat formulation combinationsranging from 5.41 to 5.78. T statistics compari-sons between F1 and F2 did not show any signifi-cant difference in pH except for 85r (Table 2). As

Table 1 Pasteurization processes in minutes for sousvide rendang computed using graphical method

Temperature(°C)

Mode ofheating†

Pasteurizationprocess (min) CUT*

75 Slow 478 45Fast 443 2

80 Slow 180 47Fast 161 2

85 Slow 96 51Fast 88 2

90 Slow 70 55Fast 29 2

*CUT, come-up time; time required in minutes forwater at room temperature (25 � 1°C) to reach thespecified temperature of pasteurization.†Slow heating – product added for pasteurization withwater at room temperature (25 � 1°C); fast heating –product added for pasteurization after water hasreached the specified temperature.

Table 2 Physicochemical properties of differentformulations of sous vide rendang

Sample1

pH

F1 F2 T statistic

75t 5.56 � 0.02 5.78 � 0.02 4.7875r 5.55 � 0 5.56 � 0.01 1.0075k 5.51 � 0.06 5.56 � 0.04 2.5085t 5.61 � 0.04 5.76 � 0.03 2.1485r 5.53 � 0.03 5.59 � 0.04 11.00*58k 5.41 � 0.14 5.54 � 0.005 1.00

Water activity

F1 F2 T statistic

75t 0.96 � 0.01 0.94 � 0.005 59.00**75r 0.97 � 0.01 0.96 � 0.01 7.0075k 0.98 � 0.01 0.97 � 0.005 0.5985t 0.97 � 0.01 0.94 � 0 4.7385r 0.97 � 0.01 0.95 � 0.003 1.8658k 0.97 � 0.01 0.96 � 0.01 0.59

Moisture content

F1 F2 T statistic

75t 58.34 � 2.57 60.32 � 6.25 0.5475r 59.43 � 2.76 58.01 � 6.64 0.3675k 59.19 � 2.69 58.78 � 4.89 0.1985t 58.50 � 2.23 56.74 � 9.6 0.2485r 58.90 � 1.89 58.63 � 6.98 0.0558k 58.26 � 1.88 58.96 � 9.37 0.09

175, processing at 75°C for 8 h; 85, processing at 85°Cfor 2 h; *, significant (P < 0.05); **, highly significant(P < 0.001).F1, formulation 1; F2, formulation 2; k, knuckle (m.quadriceps femoris); r, rump (m. biceps femoris); t,topside (m. semimembranosus).




one of the controlling factors associated with thesafety of SV products, in order to be effective, thepH must be �5.0 (UKFSA 2004). In the case of SVrendang, all values obtained from the combina-tions were above the specified limit of �5. Acidi-fication of the product is achievable theoreticallybut may not be realistic SV in traditional formula-tions from other states in Malaysia do not includethe addition of acids. Thus, an acidified version ofSV rendang may not be acceptable to the consum-ers. Variations of rendang recipes tend to be moreinto the addition of spices and herbs, depending onthe prevailing custom of the state. An example isrendang tok from Perak, which is incorporatedwith spices such as coriander, cumin, fennel, car-damoms, cinnamon, cloves, turmeric powder andchilli powder aside from the addition of shallots,garlic and ginger, the common ingredients ofrendang (Yew 1999).

Water activity also showed significant differ-ence (P < 0.05) between different combinationswith Aw ranging from 0.94 to 0.98. All formula-tions were 0.97 or less except for F175k at 0.98(Table 2). T statistics showed that only 75t mani-fested a significant difference in Aw for its F1 and

F2. Generally, F2 had a lower water activity com-pared with F1 irrespective of the processing andthe kind of meat used. This was attributed tolower amounts of ground ingredients in F2 com-pared with F1. Water activity is also a specificcontrolling factor (UKFSA 2004), which specifiesthat Aw be �0.97. Further studies can be con-ducted to utilize water activity as the maincontrolling factor and thereby lessen the amountof heat applied into the product.

Percent moisture content was not significantlydifferent for all the SV rendang combinations,with values ranging from 56.74 to 68.33%.Lower moisture content was also observed for F2compared with F1, the same trend observed inwater activity.

Four sensory attributes were evaluated, namely,flavour, spiciness, texture and acceptability ofthe combinations. All sensory attributes weresignificantly different (P < 0.001) for all the SVcombinations.

Figure 3 shows that flavour scores were higherin sous vide rendang using the rump part of thebeef (F275r, F185r, F285r). Flavour scores werealso higher in SV rendang processed at 85°C for

0

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10

SSF175T SSF275T SSF175R SSF275R SSF175K SSF275K SSF185T SSF285T SSF185R SSF285R SSF185K SSF285K

Treatments

Score

Flavor Spiciness Texture Acceptability

a

bcde

bc

def

aa a cde

ab

def

cd

adef

bb

b efb b

cab

bf b bb f bcd a

b

ab

bab

c c ab

bc

bc

de

abce

cc

cff

Figure 3 Sensory evaluation of different combinations of sous vide rendang. SS, sous vide; F1, formulation 1;F2, formulation 2; 75, processing at 75°C for 8 h; 85, processing at 85°C for 2 h; k, knuckle; r, rump; t,topside. a–f, Duncan Multiple Range Test (DMRT) grouping, means with different letters on the same colouredcolumns differ significantly (P < 0.001).




2 h rather than the slower process of 75°C for8 h. Generally, spiciness was observed to havehigher scores in F1 compared with F2, which isunderstandable considering that the amount ofchilli in F2 was 50% lower than F1 (Table 3).Texture was observed to be softer at 85°C pro-cessing compared with 75°C. Topside and rumpprocessed at 85°C were found to be softercompared with the knuckle part. General accept-ability was highest for F175r followed by F185tand F175t.

Results demonstrated that the application ofPv90 = 10 min, in this case the processing combi-nations of 75°C/8 h and 85°C/2 h, showed nodetrimental effect on the sensory properties ofSV rendang. The 85°C/2 h pasteurization processproduced better flavour and texture in SVrendang, whereas the rump part of the beef hadbetter flavour compared with the knuckle andtopside. Thus, processing combination and meatused for the subsequent studies were F1 insteadof F2, 85°C/2 h instead of 75°C/8 h, and rumpinstead of knuckle and topside. F1, or the originalformulation, was retained since sensory resultsindicated significantly lower sensory scores forF2.

Storage studies

No microbial growth was detected for total meso-philic anaerobic count, C. perfringens, Salmonellasp., S. aureus and total coliforms for 2CC, 2SS70,2SS85, 10SS70 and 10SS85. However, growthwas observed for B. cereus and L. monocytogeneson day 35 of analysis for the conventionallycooked rendang stored at 10°C or 10CC (Fig. 4).Microbial growth was limited to 3 log cfu/g forboth microorganisms. Physicochemical propertiesshowed no untoward changes for both pH and Aw

(Fig. 5). Although a decreasing trend for Aw wasobserved during storage, no significant difference(P < 0.05) was observed for Aw and similarly forpH.

SV rendang can last up to day 35 for the threeprocessing conditions (CC, SS70 and SS85) storedat 2°C; however, only rendang processed via SV(SS70 and SS85) was microbiologically stableat 10°C. Conventionally cooked (CC) productstored at 10°C had a maximum shelf life of 21days based on the growth of microorganisms.

Heat treatment applied for SS85 in combinationwith storage at <8°C gave a protection factor of 6with respect to spores of psychrotrophic C. botu-linum (UKFSA 2004). At this point, guidelinesallow the shelf life of 40 days maximum for thisproduct. If a higher shelf life is required (>40days), a challenge test will have to be conductedto determine the actual shelf life of the product.SS70 or Pv70 = 1 min is theoretically given a shelflife of 21 days, according to the French regula-tions (Church & Parsons 1993). However, thefact that only the chilling temperatures of 2°C metwith the guidelines means that the rule stillapplies that shelf life for these products will onlybe considered within 10 days (Peck et al. 2006).Other than that, a challenge test will have to beconducted to establish maximum shelf life.

Targeting for C. botulinum may mean a verysafe product at the expense of the sensory prop-erties of the food. In this case, SV rendang pro-cessed to meet the requirements of UKFSA didnot have any detrimental effects on its sensory

A Bacillus cereus

0

1

2

3

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6

0 5 10 15 20 25 30 35 40

log

cfu

/g

2CC 2SS70 2SS85

10CC 10SS70 10SS85

B Listeria monocytogenes

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3

4

5

6

0 5 10 15 20 25 30 35 40no of days

no of days

log

cfu

/g

2CC 2SS70 2SS85

10CC 10SS70 10SS85

Figure 4 Microbiological quality of stored sous viderendang at 2 and 10°C. 2CC, stored at 2°C, conven-tional cooking; 2SS70, stored at 2°C, sous vide 70°C/100 min; 2SS85, stored at 2°C, sous vide 85°C/2 h.10CC, stored at 10°C, conventional cooking; 10SS70,stored at 10°C, sous vide 70°C/100 min; 10SS85,stored at 10°C, sous vide 85°C/2 h.




Table 3 Sensory evaluation of thedifferent combinations of sousvide rendang

75t1

F1 F2 T statistic

Flavour 5.10 � 0.51 5.47 � 0.38 0.85Spicy 6.26 � 0.19 2.35 � 0.35 16.90**Texture 3.97 � 0.62 3.39 � 0.38 2.85Acceptability 6.8 � 0.43 6.18 � 0.35 1.65

75r

F1 F2 T statistic

Flavour 5.45 � 0.67 6.96 � 0.43 3.91*Spicy 6.96 � 0.55 4.42 � 0.50 5.00*Texture 3.87 � 0.50 3.20 � 0.71 1.46Acceptability 8.87 � 0.71 5.99 � 0.79 5.42*

75k

F1 F2 T statistic

Flavour 5.45 � 0.36 5.22 � 0.07 1.11Spicy 4.68 � 0.63 3.35 � 0.25 3.47*Texture 3.59 � 0.8 4.25 � 0.18 1.39Acceptability 5.22 � 0.44 5.71 � 0.34 1.77

85t

F1 F2 T statistic

Flavour 5.16 � 0.68 4.85 � 0.87 1.20Spicy 6.44 � 0.44 3.59 � 0.36 16.50**Texture 2.79 � 0.52 2.64 � 0.40 0.39Acceptability 7.30 � 0.64 5.96 � 0.46 4.41*

85r

F1 F2 T statistic

Flavour 7.63 � 0.79 6.59 � 0.67 0.78Spicy 6.19 � 0.56 4.12 � 0.79 3.12*Texture 2.58 � 0.18 4.01 � 0.79 3.53*Acceptability 6.29 � 0.22 6.48 � 0.48 0.79

85k

F1 F2 T statistic

Flavour 5.35 � 0.35 5.08 � 0.48 1.78Spicy 4.7 � 0.34 2.13 � 0.16 19.52**Texture 3.91 � 0.3 3.39 � 0.28 3.35*Acceptability 5.31 � 0.32 5.66 � 0.38 1.49

175, processing at 75°C for 8 h; 85, processing at 85°C for 2 h.F1, formulation 1; F2, formulation 2; k, knuckle (m. quadriceps femoris); r,rump (m. biceps femoris); t, topside (m. semimembranosus); *, significant(P < 0.05); **, highly significant (P < 0.001).




properties. For other foods that may not reactfavourably to SV processing at these levels, otherpossibilities may be considered. One is to modifythe formulation to lower the water activity. Theother is to lower the pH, but this may not beapplicable to most recipes of Malaysia. Anotherpossibility is to incorporate spices with antimicro-bial properties to the formulation since Malaysiancuisine is known for being spicy.

SV processing for Malaysian cuisine is a prom-ising scenario as seen from this study.

Conclusions

SV rendang may be pasteurized for 443 min at75°C, 161 min for 80°C, 88 min for 85°C and29 min for 90°C using fast heating to meetthe Pv90 = 10 min guideline for pasteurization.Process-meat-formulation combinations of SV

rendang indicated that processing at 85°C/2 h,the use of rump and F1 produced better sensoryproperties. Aw, aside from pasteurization, is a pos-sible controlling factor for SV rendang but notpH. Growth of B. cereus and L. monocytogeneswas observed during day 35 for 10CC only. Con-ventionally cooked rendang stored at 2°C and SVrendang (SS70 and SS85) stored at 2 and 10°Ccan last for 35 days using microbiological countas its storage indicator. Applications of guidelinesby UKFSA would mean that maximum shelf lifeallowable for CC and SS70 will only be 10 dayscompared to SS85, which is 40 days.

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A

0.966

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0.97

0.972

0.974

0.976

0.978

0.98

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no of days

Aw

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0 40302010

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B

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5.65

5.70

5.75

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no of days

pH

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10SS70 10SS85

Figure 5 Physicochemical changes associated withstorage of sous vide rendang at 2 and 10°C. 2CC,stored at 2°C, conventional cooking; 2SS70, stored at2°C, sous vide 70°C/100 min; 2SS85, stored at 2°C,sous vide 85°C/2 h; 10CC, stored at 10°C, conven-tional cooking; 10SS70, stored at 10°C, sous vide70°C/100 min; 10SS85, stored at 10°C, sousvide 85°C/2 h. Aw, water activity.




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