A consumer and a trained descriptive panel was utilized to determine liking ratings and flavor profiles, respectively, for commercial brands of pre-stirred yogurt. Once the consumer and descriptive panel data was collected, the data was combined to determine the interrelationship of these two sets of data and to determine the conditions necessary to optimize the sensory characteristics of commercial yogurt. This study was broken down into two parts: (1) evaluation by a 90 to 182 member consumer panel and an 11 member descriptive panel for 14 strawberry and 6 lemon yogurt brands, and (2) correlation of the sensory measures of sweetness and sourness, and analytical measures of sugars and acids for 14 strawberry, 12 raspberry, 6 lemon, and 17 plain yogurt brands. Large sensory differences were found between yogurts for both flavors (strawberry and lemon) by both panels. Correlation and principal component analysis (PCA) indicated that two distinct groups of descriptors contributed to the liking of the yogurts: one associated with the fruity and sweetness characteristics, and the other related to the plain yogurt and sourness descriptors. Consumers based their overall liking ratings on fruit flavor, sweetness, sourness, and a balance of sweetness/sourness liking. Males and females rated samples differently by as much as one full scale value on a 9-pt. hedonic scale. Use of PCA to relate the two panels revealed that high consumer acceptance corresponded with the PC loaded with fruity and sweet characteristics while lower consumer acceptability was noted with high loadings on PC2 which was comprised of plain yogurt, acetaldehyde, and sourness descriptors. The results from the first part of the study indicate that to produce a highly acceptable yogurt, processors should strive to provide a balance between sweetness and sourness and provide enough fruit flavor to mask plain yogurt characteristics. In the second part of this study, titratable acidity and pH were measured for all the yogurts, while sugars were measured by HPLC only for the fruit flavored yogurts. Consumer overall liking was significantly correlated with sweetness intensity, sweetness:sourness (sw:so) ratio, and the summed impact of sweetness and sourness from the trained panel for strawberry and raspberry yogurt. No correlations between analytical measures and overall liking were found for any of the yogurts. A sw:so ratio greater than 1.0 for strawberry, and .8 for raspberry and lemon appeared necessary for high consumer acceptance. Generally, it was found that the sweeter the yogurt, the higher the consumer acceptance of fruit flavored yogurt. No relationships were found for any sensory and analytical measures for predicting the overall liking of plain yogurt. However, the best predictors of consumer liking of fruit flavored yogurt were the descriptive panel ratings. / Graduation date: 1991

Graduation date: 1993

Thesis (M.Tech.: Food Technology)-Dept. of Biotechnology, Durban University of Technology, 2007 xiii, 100 leaves / There are many ways for milk and dairy products to develop flavour defects. Sensory evaluation, has been the traditional approach to characterize off flavours. The need for odour sensing devices becomes greater when volatile and semi-volatile organic compounds are present in the product in parts per billion or even in the parts per trillion concentration range that cause off flavours. Today, sophisticated, sensitive instrumental tests such as electronic nose technology coupled with gas chromatography are capable of detecting, identifying and quantifying the specific chemical agents responsible for off flavours. This study focused on the use of the electronic nose as a novel technology for the detection and monitoring of milk quality by testing the effects of heat treatment at 63˚C and shelf life. Microbiological testing, sensory evaluation and gas chromatographic analysis were carried out together with aroma profiling using the electronic nose to determine milk quality.

Thesis (M.Tech.: Food Technology)-Dept. of Biotechnology, Durban University of Technology, 2007 xiii, 100 leaves / There are many ways for milk and dairy products to develop flavour defects. Sensory evaluation, has been the traditional approach to characterize off flavours. The need for odour sensing devices becomes greater when volatile and semi-volatile organic compounds are present in the product in parts per billion or even in the parts per trillion concentration range that cause off flavours. Today, sophisticated, sensitive instrumental tests such as electronic nose technology coupled with gas chromatography are capable of detecting, identifying and quantifying the specific chemical agents responsible for off flavours. This study focused on the use of the electronic nose as a novel technology for the detection and monitoring of milk quality by testing the effects of heat treatment at 63˚C and shelf life. Microbiological testing, sensory evaluation and gas chromatographic analysis were carried out together with aroma profiling using the electronic nose to determine milk quality.