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.

The Effect of High-Intensity Ultrasound on the Physicochemical and Microbiological Properties of Mexican Panela Cheese

“…Some researchers have found a reduction in micelle size, greater denaturation of serum proteins, and better gel firmness [11][12][13]. Others have shown a delay in serum separation and an increase in viscosity [14], as well as an improvement in the gel set time and firmness when the pH of milk is modified to 8.0 before the application of HIU [12,15]. Liu et al [12] studied the effects of HIU on skim milk made by reconstitution of skim milk powder, with a treatment of 20 kHz at 30 • C. They found an improvement in the gelatinization and firmness of the curd when the pH of the ultrasound-treated milk was 8 and was re-adjusted back to 6.7.…”

Applications of ultrasound in processing of liquid foods: A review

“…Ultrasonically treated milk samples also showed an increase in the gel firmness, coagulum strength, final storage modulus, cohesiveness and water holding capacity [52]. These factors were stated to be due to a decrease in the soluble proteins and an increase of insoluble high molecular weight co-aggregates formed as a result of protein denaturation on sonication [52][53][54]. In these cases once again 20 kHz was the favoured frequency of sonication.…”

“…This effect was greatest at the lowest treatment frequencies and may be used to produce a product which has different properties to that of thermally treated milk in addition to a more efficient manufacturing process. Ultrasonically treated milk samples also showed an increase in the gel firmness, coagulum strength, final storage modulus, cohesiveness and water holding capacity [52]. These factors were stated to be due to a decrease in the soluble proteins and an increase of insoluble high molecular weight co-aggregates formed as a result of protein denaturation on sonication [52][53][54].…”

Three Pillars of Novel Nonthermal Food Technologies: Food Safety, Quality, and Environment

“…Ultrasonically treated milk and yogurt samples also showed an increase in the gel firmness, coagulum strength, final storage modulus, cohesiveness, and water holding capacity [152]. ese factors were stated to be due to a decrease in the soluble proteins and an increase in insoluble high-molecular-weight coaggregates formed as a result of protein denaturization on sonication [153,154].…”