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In this study, lutein Pigment (0.07, 0.13 and 0.2 %w/w ) and whey protein concentrate (0.2, 0.3 and 0.4 %w/w) were added to the milk.  Qualitative characteristics of yogurt samples were analysed regarding physico-chemical, microbiological, textural and sensory properties over 21 days. Adding whey protein concentrate and lutein, lowered the level of synersis and acidity but increased the amount of dry matter, fat, viscosity and pH of yogurt samples. According to the results of microbe analysis, there was not any evidence of the growth of mold, yeast and coliform bacteria in the samples. In the case of sensory properties, adding whey protein concentrate and lutein, raised the scores of texture, mouthfeel evaluation and lowered the scores of appearance evaluation. Among all treatments, yogurt containing 0.2 %, w/w whey protein concentrate and 0.07 %, pigment lutein earned the best score with respect to overall flavor and quality acceptability.   

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Abstract

Doogh is a fermented dairy drink that produced with mixing of pasteurized yogurt, water, essential oils and salt. Due to low pH, doogh is susceptible to spoilage with mold and yeast that is the main challenge for its shelf life. At the same time, the consistency is very important in quality and marketability of doogh. Nowadays, the interesting of consumers to natural antimicrobial substances rather than chemical preservatives has been progressively increased. Chitosan is a derivative of chitin, unlike synthetic polymer compounds, is non-toxic and biodegradable in nature. The aim of this study was investigation on the effect of chitosan on the qualitative features and shelf life of doogh. In this research, chitosan was added to the doogh in four levels (0.05, 0.1, 0.2, 0.3%) and qualitative characteristics of them were investigated by physico-chemical, microbiological and sensory analysis during 60 days. The results showed that, use of chitosan resulted decreasing of phase separation rate, acidity, mold and yeast, Streptococcus salivarius subspecies thermophilus and Lactobacillus delbrueckii subspecies bulgaricus counts and increasing of viscosity and pH. So that, samples containing 0.3% chitosan had 97% decrease in phase separation rate, 24% decrease in acidity, 6% decrease in mold and yeast count, 19% decrease in Streptococcus salivarius count, 11% decrease in Lactobacillus delbrueckii count, 122% increase in viscosity and 15% increase in pH compared with control samples, at the last day of storage. In the case of sensory features, chitosan did not have any effect on the color and appearance of doogh, but had effect on the flavor and also consistency was improved.

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The target of present study was production of functional low-fat yogurt fortified with flaxseed flour. The effect of different concentrations of flaxseed flour (0.5, 1 and 1.5%) during different storage time (1, 7, 14, 21 days) have been studied on physicochemical, microbial and sensory properties of Low fat yogurt. The results showed that increasing in flaxseed flour had no significant effect on pH, acidity and peroxide value while significantly synergies and dry matter increased and pH and viscosity decreased. With increasing in storage time, dry matter and Acidity increased, while pH and viscosity decreased. Peroxide values increased significantly during storage of yogurt samples. Different levels of flaxseed flour had no significant effect on mold and yeast counts, while it has showed significant increase with increasing in storage time. Regarding to sensory properties, the most scores were obtained for control and with 0.5% flaxseed flour samples. while scores were reduced during storage. Regarding to nutritional properties of flaxseed flour and including essential fatty acids, addition of 0.5% flaxseed flour with preserving chemical and physical properties can help to produce functional low fat yogurt.