Flavor and Sensory Characteristics of Yogurt Derived from Milk Treated by High Intensity Ultrasound

Abstract

High intensity ultrasound (US) treatment has been proven to homogenize milk and reduce its microbial load while simultaneously assist in the formation of volatiles that affect its flavor and aroma. Additionally, high intensity US treatment has positive effect on the formation of yogurt curd and improve some of its quality and sensory characteristics. The current work aims to the study the sensory characteristics of yogurt produced from milk treated by high intensity US, furthermore to characterize the volatile components produced during fermentation process. Yogurt samples were produced by bovine milk (3,5% fat content and 3,3% protein content) that was previously ultrasonicated (frequency of 20 kHz and intensity range 150–750 W) for 10 min, using industrial starter culture (Streptococcus thermophilus and Lactobacillus delbrueckii subsp. Bulgaricus). After the end of fermentation process (pH = 4,7) samples were stored at 4 °C overnight. Volatile components were analyzed by using solid phase microextraction headspace analysis in combination with gas chromatography/mass spectrometry. The compounds that were identified belonged mostly to three categories carboxylic acids (hexanoic acid, octanoic acid), ketones (2,3 butadienone, 2-heptanone, 2-nonanone) and aliphatic hydrocarbons. Sensory evaluation was conducted on the yogurt samples for flavor, texture and overall acceptance. Results proved that milk treated by high intensity US led to acceptable yogurt with superior texture characteristics (cohesiveness, hardness, firmness) and inferior taste and flavor (off flavors). The volatile compounds that affect aroma and flavor are formed during the US treatments of the milk, due to high localized temperature and cavitation phenomena as well as during fermentation.