Master of Science

La matrice du fromage Cheddar est souvent, selon les souches, un milieu propice à la survie des probiotiques au cours de la fabrication et de l’entreposage à long terme. Elle les protégerait également lors du passage dans le tractus gastro-intestinal, leur permettant d’atteindre l’intestin sous une forme viable. Par contre, la compétition avec les lactocoques pour les nutriments, le pH acide, le sel et la présence d’oxygène pendant la fabrication sont tous des facteurs qui peuvent affecter la viabilité des probiotiques. Dans le but de vérifier les paramètres influençant la viabilité des probiotiques dans le fromage Cheddar pendant la fabrication et la maturation, six souches probiotiques commerciales ont été sélectionnées. Il s’agit des souches Lactobacillus rhamnosus GR-1, Lb. rhamnosus GG, Lb. rhamnosus R0011, Lactobacillus helveticus R0052, Lactobacillus acidophilus LA-5 et Bifidobacterium animalis ssp. lactis Bb-12. Dans un premier temps, afin de déterminer la nature des interactions possibles avec les lactocoques de fabrication, une étude de biocompatibilité a été effectuée avec quatre souches de lactocoques commerciaux ainsi qu’un mélange de lactocoques commerciaux. Il s’est avéré que la biocompatibilité des probiotiques était variable en fonction du lactocoque. Le lactocoque W62 était le plus biocompatible pour les souches probiotiques. Dans l’extrait acellulaire de la souche W62, la combinaison des souches Bb-12 et GR-1 était plus performante. La viabilité des six souches probiotiques seules et des souches Bb-12 et GR-1 fut ensuite évaluée dans des caillés modèles composés du lactocoque (W62), de deux pH (5.0 et 5.4) et de deux S/H (2.5 % et 4.5 %). Chacune des souches probiotiques étaient affectées différemment en fonction du pH, du S/H et de la présence de la souche W62. Dans les caillés modèles, la viabilité des souches de Lb. rhamnosus (GR-1, GG et R0011) était meilleure que celle des souches Lb. acidophilus LA-5, B. lactis Bb-12 et Lb. helveticus R0052. Lors de leur co-culture, la population des souches Bb-12 et GR-1 était plus élevée que lorsqu’elles étaient seules. Des fromages furent ensuite fabriqués avec ces deux souches seules ou en combinaison. Pendant la fabrication fromagère, la viabilité de la souche Bb-12 diminua de 1 log UFC/g pendant la cuisson. Des essais en mini-fromagerie confirmèrent qu’une agitation élevée pendant la cuisson diminuait la survie de la souche Bb-12. Par contre, il fut impossible de confirmer si l’oxygène était aussi en cause. Pendant l’affinage des fromages, les deux souches probiotiques ont maintenu leur population dans les fromages pendant les douze semaines d’affinage. La protéolyse ainsi que la quantité d’acides organiques étaient plus élevées dans les fromages contenant la souche GR-1. Le fromage contenant la souche Bb-12 entreposée à 4°C avait des propriétés sensorielles différentes des fromages contenant la souche GR-1. / When added to Cheddar cheese, viability of probiotic strains vary according to combination of several factors. These factors are the probiotic strain being studied, the lactic acid bacteria strain used in the manufacture of cheese, the presence of other probiotic strains, stirring while cooking, pH, salt on moisture (S/M) content and ripening temperature. The lactic acid bacteria strain used for Cheddar cheese process influence the viability of probiotic strains. In the same way, co-culture of two probiotic strains can also affect their viability. While cooking procedure, high level of agitation may affect probiotic strain viability. During ripening, each probiotic strain had a single survival profile according to the pH, S/M and ripening temperature. Moreover, depending on the probiotic strain added in cheese, proteolysis and the amount of organic acids had increase. This increase causes changes in texture and in sensory properties of Cheddar cheese.

Thesis (MAgricAdmin)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: The objective of this study was to determine the sensory characteristics of Cheddar cheese that drive consumer acceptance. In addition, it investigated whether specific sensory profiles would satisfy specific consumer segments to ultimately facilitate greater acceptance and consumption of Cheddar cheese. A trained panel applied descriptive sensory analysis (DSA) to characterise the sensory attributes of six commercially produced cheeses ranging in maturity from 1 to 32 months. The cheese samples were differentiated by appearance, aroma, flavour and textural attributes. A consumer panel comprising of 115 target consumers rated preference for the cheeses on a 9-point hedonic scale. Moreover consumers completed a screener designed to collect socio-demographic information and opinions on cheese and cheese products. Instrumental colour analysis was performed on the cheese samples and in-depth consumer opinions and attitudes towards cheese were examined using the focus group technique. Analysis of variance (ANOVA) was conducted on the sensory and instrumental data, as well as the consumer liking and perception data. Additionally, a t-test was performed at a 5% significance level to determine the direction of the difference between the mean values. Multivariate analyses were performed on the sensory and consumer data to determine whether relationships existed between sample attributes and consumer liking. Consumer acceptability scores were segmented by agglomerative hierarchical clustering (AHC) using Ward’s test. ANOVA was performed on the consumer data per cluster for colour liking, texture liking, flavour liking and overall liking. Partial least squares regression (PLS) was performed in an attempt to relate consumer degree of liking data, the socialdemographic and attitudinal data, as well as the sensory and instrumental data. The younger cheeses; Gouda at one month, Edam at two months and Cheddar at 4 months were characterised as glossy, with a buttery and creamy aroma; creamy flavour, salty and slightly sour taste combined with lingering cheese flavour. Textures were described as creamy, springy and rubbery. Sensory attributes of visible white crystals, moisture seepage, brothy and Cheddar aromas; brothy, Cheddar and prickle flavours together with textural attributes of firm, hard, crumbly, grainy and teeth-coating characterised the aged Cheddar cheeses. Flavour development was not progressive as the cheeses aged and atypical flavour development was identified in the Cheddar cheese aged to 8 and 15 months, respectively. Flavour followed by price and convenience drive cheese purchase amongst this group of consumers. From a sensory perspective, glossy appearance, a red hue and yellow colour drive cheese colour liking. Texture liking is driven by springy and hard attributes. Flavour liking is driven by cooked milk, buttery and creamy aroma and creamy flavour. Finally overall cheese liking is driven by glossy appearance; cooked milk, buttery and creamy aroma; creamy flavour; springy and creamy texture; specific instrumental colour values, as well as fat, moisture and salt content. Three clusters per variable of colour, texture, flavour and overall liking of cheese were identified through segmentation performed on the preference data. Results indicate that consumers are not homogenous in their sensory requirements, attitudes and behaviour towards cheese. Based on the consumer preference for specific sensory characteristics of cheese, consumer segments can be identified and cheese can be optimised to satisfy these sensory requirements. / AFRIKAANSE OPSOMMING: Die doel van hierdie studie was eerstens om te bepaal watter spesifieke sensoriese eienskappe van Cheddarkaas verbruikersaanvaarbaarheid dryf, en tweedens om verbruikersdata te segmenteer ten einde vas te stel of verskillende verbruikersegmente verskillende voorkeure het wat betref Cheddarkaas. Kennis hiervan sal uiteindelik bydra tot verhoogde verbruikerstevredentheid, en dus verhoogde verkope van Cheddarkaas op die plaaslike mark. Beskrywende sensoriese analise en ’n opgeleide paneel is gebruik om die sensoriese eienskappe van ses kommersiële kaas variante te bepaal. Instrumentele kleuranalise is ook bepaal. Die monsters kaas het gewissel in ouderdom (van 1 tot 32 maande veroudering), asook in voorkoms, aroma, geur, smaak en teksturele eienskappe. ’n Verbruikerspaneel bestaande uit 115 individue het die voorkeur en aanvaarbaarheid van die ses variante kaas ge-evalueer deur gebruik te maak van die 9-punt hedoniese skaal. Sosio-demografiese inligting en verbruikeropinies betreffende kaas is ook versamel. Ten laaste is die fokusgroep tegniek gebruik om in-diepte inligting te verkry wat betref verbruikeropinies en –houdings ten opsigte van Cheddarkaas. Analise van variansie (ANOVA) is op sensoriese, instrumentele en verbruikersdata toegepas. T-toets is by ‘n betekenispeil van 5% uitgevoer om te bepaal of daar per eienskap betekenisvolle verskille tussen monstergemiddeldes was. Meerveranderlike analise is uitgevoer op die sensoriese en verbruikerdata ten einde te bepaal of spesifieke sensoriese produkeienskappe verbruikersvoorkeur dryf. Ward se statistiese groepering is gebruik om te bepaal of die verbruikers in verskillende voorkeursegmente gegroepeer kan word. Hierna is ANOVA op elke segment uitgevoer ten einde per segment verbruikersvoorkeur van die onderskeie produkte te bepaal wat betref voorkoms, geur en tekstuur. Meervoudige regressie analise is toegepas om die verwantskap tussen verbruikervoorkeur-, houding- en sosio-demografiese eienskappe van die verbruikers te bepaal, asook tussen die sensoriese en instrumentele produkeienskappe. Die kase wat vir ‘n kort tydperk verouder is, m.a.w. Gouda, Edam en Cheddar na 4 maande veroudering is beskryf as glansend, met ‘n ryk botter en romerige aroma, romerige geur, sout en effense suur smaak, asook ‘n standhoudende kaasgeur. Teksturele eienskappe van hierdie drie kaassoorte is beskryf as romerig, veerkragtig en effe rubberig. Die Cheddar kase wat langer verouder is, het tekens getoon van sigbare wit kristalle en sinerese op die kaasoppervlak, ‘n prikgevoel op die tong, asook sopagtige (“brothy”) en Cheddaragtige aromas en geure. Die teksturele eienskappe van die verouderde Cheddar kase is beskryf as ferm, hard, krummelagtig en greinerig, asook met’n geneigdheid van die kaas om aan die tande vas te kleef. Geurontwikkeling het nie progressief plaasgevind soos die kase verouder het nie. Die Cheddar kase wat onderskeidelik vir 8 en 15 maande verouder is, het atipiese geurontwikkeling getoon. Belangrike faktore wat tydens die aankoop van kaas’n rol speel, en dus voorkeur dryf is eerstens geur, tweedens prys en derdens produk-gemak. Sensoriese aspekte wat voorkeur dryf, is ‘’n glansende voorkoms en effe rooierige-gelerige kleur. Tekstuur voorkeure sluit in veerkragtiheid en hardheid, terwyl geur voorkeure die volgende insluit: romerige, botterige en melk aromas, asook ‘n romerige geur. In die geheel gesien, dryf die volgende eienskappe dus verbruikersvoorkeur: kaas met ‘n glansende voorkoms, geure soos botteragtig, roomagtig en melkerig en teksture soos veerkragtig en romerig. Voedinstofinhoud beȉnvloed ook verbruikersvoorkeur, nl. soutinhoud, vetinhoud en voginhoud. Segmentasie van verbruikersdata het getoon dat die onderskeie verbruikersegmente nie ooreenstem wat betref hul verbruikersvoorkeure, houdings en persepsies van kaassorte nie. Die resultate het egter spesifike sensoriese rigtingwysers geidentifiseer wat die bedryf kan gebruik om kaas te produseer vir elk van die onderskeie marksegmente.

Thesis (M.S.)--Mississippi State University. Department of Food Science, Nutrition and Health Promotion. / Title from title screen. Includes bibliographical references.

A linear diffusion test in sedimentation tubes filled with caseinagar gel successfully measured milk clotting enzymes at concentrations of 10-4 to 1 X 10-l rennin units/ml with 95% accuracy. Diffusion rates were unaffected by diluting enzyme samples with whey, 3% NaCl, and water, The distribution of rennet, porcine pepsin, mucor pusillus var Lindt (MP) protease, and rennet-pepsin mixtures between curd and whey was determined on milk coagulated at pH 5.2, 6.0, 6.4, and 6.6. The procedure accounted for 100 + 7% of the added enzymes. The distribution of rennet was pH dependent with 31% and 72% in curd and whey respectively at pH 6.6, and 864 and 174 respectively at pH 5.2. The distribution of MP protease was independent of pH with approximately 154 and 85% in the curd and whey at all pH values. Pepsin behaved similar to rennet but was unstable above pH 6.0. During Cheddar cheese making, 7% and 58% of the original rennet, 6% and 93% of the original MP protease, and 5% and 17% of the original rennet-pepsin mix was active in the curd and whey respectively at dipping. After overnight pressing, 6% of the rennet, 3% of MP protease, and 4% of the rennet-pepsin mix remained active in the cheese. At dipping only 9% of the original pepsin was detected in the whey. Pepsin was unstable at pH values used to release the enzyme from the curd and could not be quantitated.

The objectives of this research were to compare different types of cocoa and chocolates in the formulation of processed chocolate cheese and aged Cheddar cheese, and to evaluate sensory, physical, chemical and quality parameters of each. Four different varieties of chocolates were utilized along with other ingredients to prepare processed chocolate cheeses and were tested for consumer acceptability for their basic and critical attributes. Chocolate chips of four different types and proportions were incorporated into Cheddar cheese curd, ripened for 105 days, and a trained panel evaluated the sensory parameters. Results indicated that processed chocolate cheese made with Bordeaux chocolate was preferred the most by consumers, followed by those prepared with Ghirardelli, German and Dutch chocolates, respectively. This research provides a platform to pioneer the study of the sensory profiles of the processed chocolate cheeses. Development of a lexiconal study for the Cheddar cheeses with chocolate chips is also necessitated.

Published Article / An artificial neural network (ANN) that is able to distinguish between Cheddar cheese produced with milk from mixed and single breed sources was designed. Samples of each batch (4 pure Ayrshire/4 mixed with no Ayrshire milk) were ripened for 92 days and analysed every 14 days. A novel ANN was designed and applied which, based only on Lactococcus lactis counts, provided an acceptable classification of the cheeses. The ANN consisted of a multi-layered network with supervised training arranged in an ordered hierarchy of layers, in which connections were allowed only between nodes in immediately adjacent layers.

During the course of ripening, Cheddar cheese frequently develops a flavor defect described as fruity. Recent work has indicated that the use of certain starter cultures ultimately results in the development of the defect as the cheese ages. The flavor compounds responsible for the defect, however, have not been elaborated. The purpose of this investigation was to isolate and identify the components responsible for the fruity flavor defect and to evaluate the role of certain cheese starter cultures in the development of the defect. Since the fruity character of the defect is apparent in the aroma of the cheese, the compounds responsible for the defect were expected to be reasonably volatile. Volatile constituents were isolated by a distillation technique from fat expressed from a typically fruity cheese by centrifugation. The volatile constituents were then separated by gas-liquid chromatography. By monitoring the odor of the effluent stream of the column, it was possible to determine which components had fruity odors, and these were subsequently identified by mass spectral analysis and coincidence of retention time with the authentic compounds. Ethyl butyrate, ethyl hexanoate, and ethyl octanoate were found to be the only compounds with detectable fruity odors. The volatiles from the fat of four cheeses possessing varying degrees of the defect and their matching non-fruity controls were analyzed by a gas entrainment, on-column trapping, gas-liquid chromatographic technique. The manufacturing and curing conditions of each fruity cheese and its matching control were identical, except for the use of different starter cultures. Ethanol, ethyl butyrate, and ethyl hexanoate were more abundant in each of the fruity samples. The approximate concentration range of these compounds was as follows: In fruity cheese; ethanol 400 to 2,040 ppm, ethyl butyrate 1.6 to 24 ppm, ethyl hexanoate 0.9 to 25 ppm. In non-fruity cheese; ethanol 36 to 320 ppm, ethyl butyrate 0.7 to 4.7 ppm, ethyl hexanoate 0.3 to 2.2 ppm. In ten commercial Cheddar cheeses selected at random from the market, the concentration of ethanol ranged from 5.5 to 620 ppm. Single-strain cultures of Streptococcus lactis, Streptococcus diacetilactis, and Streptocococcus cremoris as well as three mixedstrain commercial cultures were evaluated for ethanol and acetaldehyde production in non-fat milk medium. Among the single-strain cultures there appeared to be no correlation between ethanol production and species, although considerable variation was noted for strains within a species. The mixed-strain cultures were designated A, B, and C. Cultures B and C had been implicated in the development of the fruity flavor defect in Cheddar cheese, while culture A produced normal cheese of good quality. Cultures B and C produced approximately 40 times more ethanol than culture A when incubated in non-fat milk medium for one month at 7°C. Certain single-strain cultures and the three mixed-strain cultures were tested for their ability to reduce acetaldehyde and propanal, and to catalyze the formation of ethyl butyrate when ethanol and butyric acid were provided as substrates. Acetaldehyde and propanal were reduced to the corresponding alcohols by all cultures, but the formation of ethyl butyrate was not observed in any culture. A good correlation between high levels of ethanol and high levels of ethyl butyrate and ethyl hexanoate in the fruity cheeses suggests that the quantity of ethanol present in the cheese may determine the amount of ester formed. Further, starters resulting in the defect produced considerably more ethanol than cultures resulting in normal cheese when incubated at 7°C, a normal temperature for curing Cheddar cheese. This observation adds weight to the hypothesis that certain cultures are directly responsible for the defect. / Graduation date: 1966

The optimization of powder x-ray diffraction (PXRD) for the study of cheese crystals was the focus of this study. A survey was conducted of various manifestations of calcium lactate crystals on the rindless surface and within mechanical openings of Cheddar cheese using PXRD. The diffraction reference card database contained a card that was entitled calcium lactate pentahydrate and corresponded to some of the crystalline material found on the cheeses. Diffractions patterns generated from other samples of crystalline material revealed the existence of an unknown crystal that resembled and behaved similarly to calcium lactate pentahydrate, but did not match the reference card. The existence of two enantiomeric variants of calcium lactate pentahydrate had been firmly established; an experiment was thus designed to determine if the unknown diffraction pattern represented one enantiomeric form, and if the ambiguously named reference card represented the other. This experiment demonstrated that the existing reference card corresponded to calcium DL-lactate pentahydrate and that the unknown diffraction pattern was generated from calcium L-lactate pentahydrate. This study resulted in the proposal of a new reference card for calcium L-lactate pentahydrate and the proposed renaming of the existing card to calcium DL-lactate pentahydrate. This discovery allows the rapid identification of both forms of calcium lactate that form in and on cheese. In order to conduct the survey and experiment that are described above, the PXRD method needed to be adjusted for use with cheese crystals. Samples of cheese crystals pose a particular challenge because they are often composed of high proportions of moisture, fat, protein, and other amorphous material; these all disrupt the efficient diffraction of crystals and thus needed to be removed or minimized. The removal of water from samples is a particular challenge because some cheese crystals contain water of hydration that may be driven off in the process, thereby destroying the crystals. A protocol for the preparation of cheese samples for PXRD was consequently developed.

Most outbreaks of foodborne illness in the United States occur as a result of improper food-handling and preparation practices in homes or food establishments. Some food-safety recommendations that are difficult to incorporate into handling and cooking procedures have contributed to a gap between food-safety knowledge and the actual behavior. The first part (Chapter 3, 4) of this study sought to ensure microbial safety by establishing alternative processing of meat products that can be easily practiced by food-operators and consumers. In Chapter 3, a novel method was developed to thaw frozen chicken-breast by submersion in hot water at 60 °C, an appropriate temperature setting for foodservice hot-holding equipment. This method is rapid (compared to either refrigerator or cold-water thawing that also uses a significant amount of water), safe, and the final cooked-product sensory-quality was not different from refrigerator-thawed and cooked product (microwave thawing results in localized overheating). Chapter 4 developed marinade-cooking (91 °C) and holding (60 °C) procedures for hamburger-patties. Frozen patties were partially grilled and finished cooking in marinade. The moderate temperature of marinade cooking overcomes the chances of thick-patties being surface-overcooked while innermost portions remain undercooked as seen in high-temperature cooking methods (grilling and pan-frying). Consumers liked the marinade-finished cooked and held patties (up to 4 h) equally or more (holding-time dependent) compared to patties grilled and held in a hot-steam cabinet. Reducing salt in perishable foods including cheese is microbial-safety concern especially in their distribution and storage. The second part (Chapter 5, 6) of this study sought to evaluate microbial safety of low-salt hard-type cheese. Aged Cheddar cheeses were inoculated with either Listeria monocytogenes (3.5 log CFU/g) or Salmonella spp. (4.0 log CFU/g) and their survival or growth was monitored at 4, 10, and 21°C for up to 90, 90, and 30 d, respectively. Low-salt (0.7% NaCl) Cheddar formulated at pH 5.1 or 5.7 exhibited no-growth or gradual reduction in L. monocytogenes and Salmonella counts. The results suggest that low-salt Cheddar is as safe as its full-salt counterparts (1.8% NaCl) and that salt may only be a minor food-safety hurdle regarding the post-aging contamination and growth of L. monocytogenes and Salmonella.