There is a growing interest on ultrasonic processing of dairy products, especially fermented dairy products which are a basis to functional foods. The studies have shown that power ultrasound can enhance the fermentation process of lactic acid bacteria by modifying their metabolic activity while reducing fermentation time and improving the quality characteristics of fermented milk products. Fermentation is one of the important stages in the processing of dairy products, but it is also one of the most time and resource consuming stages during production. Thus, the benefits of ultrasound to the fermentation process due to microbial activation become increasingly important. In fact, ultrasound applications have the dual effect on microorganisms. Besides being used for microbial activation in dairy industry, it can also be used for inactivation of microorganisms depending on ultrasound power and frequency, sonication time, microorganism type, pH, and temperature. This review article summarizes the effect of power ultrasound on microbial inactivation and microbial growth based on fermentation profile of dairy products, with a theoretical background on ultrasound, including research findings. Also, the details on the activation and inactivation mechanisms of power ultrasound to microorganisms are presented.

Recently, the demand for goat and sheep cheese has increased mainly because of its nutritional and health benefits. As a result, an enormous amount of whey from various animal species is produced as a waste/by-product. The production of functional probiotic fermented beverages from different types of whey protein concentrates (WPC) could be a good way to valorize whey. Meanwhile, reduced environmental pollution and economic sustainability will be provided. In this study, probiotic beverages enriched with 1% kiwi powder were produced from goat, sheep, and cow WPC (15%). Moreover, Streptococcus salivarius subsp. thermophilus and the probiotic bacteria Lactobacillus acidophilus and Bifidobacterium animalis subsp. lactis were used for fermentation. The results showed that WPC significantly increased the protein content and acidity of beverages (p < 0.05). Production with WPC also improved the viability of probiotic bacteria and S. thermophilus, total phenolic compound (TPC), and antioxidant activity of beverages. The highest viability of probiotic bacteria (9.67 log CFU/mL for Bb-12 and, 9.35 log CFU/mL for L. acidophilus) was found in beverages produced from goat WPC. In addition, WPC increased the free amino acid content of beverages, and the highest essential amino acids and branched-chain amino acids were found in beverages produced from goat WPC as 146.19 mg/100 g and 70.31 mg/100 g, respectively (p < 0.05). Consequently, while production with goat, cow, and sheep WPC improved quality compared to the control, beverages produced from goat WPC excelled. The production of a functional probiotic beverage with goat WPC is promising for dairy technology.

There is an increasing interest in applying fruit-processing wastes as functional food ingredients. Hazelnut skin, an interesting and innovative ingredient has recently been evaluated as one of the richest edible sources of polyphenolic compounds. This study aimed to evaluate the use of hazelnut skin as a functional additive in yogurt and to determine the effect of various percentages (2%, 3%, and 4%) of hazelnut skin on the physicochemical, microbiological, rheological, biochemical, and sensorial properties of yogurt. The results showed that the addition of hazelnut skin significantly increased total solids from 16.5% to 17.7% and fat content from 3.45% to 4.60% and decreased titratable acidity by up to 36%. The enrichment with hazelnut skin also improved the viability of yogurt bacteria, water holding capacity (WHC), and antioxidant activity of yogurts. Better results for WHC and antioxidant values were found in yogurt enriched with 4% hazelnut skin. Total phenolic content and Fe²⁺ chelating activity of yogurts increased with the increasing hazelnut skin ratio. However, yogurts with hazelnut skin had low instrumental texture parameters and apparent viscosity values. On the other hand, acceptable sensorial properties similar to control yogurts increase the consumption potential of yogurts enriched with hazelnut skin.