Honey is a highly viscous product with a unique flavor, aroma, color and texture. Honey consists of glucose, fructose, water, maltose, trisaccharides and other carbohydrates, sucrose, minerals, proteins, vitamins and enzymes, yeast and other heat-resistant microorganisms and a small amount of organic acids. Honey contains a large amount of tetracycline, phenolic compounds and hydrogen peroxide, which is antibacterial.
Honey contains starch digestive enzymes. Amylase is sensitive to heat and easily inactivated, so amylase activity is an important quality indicator of honey. The main enzymes include invertase (α-glucosidase), amylase (α-amylase) and glucose oxidase. Amylase hydrolyzes carbohydrates and is easy to digest. Invertase hydrolyzes sucrose and maltose into glucose and fructose. Glucose oxidase catalyzes the formation of glucose acid and hydrogen peroxide by glucose. Honey also contains catalase and acid phosphatase. The activity of this enzyme is usually measured as the activity of amylase and expressed as the number of amylases (DN). The honey standard specifies a minimum of 8 for DN in processed honey.
The extracted honey contains undesirable substances such as yeast (usually sugar-tolerant yeast, sugar yeast) and other heat-resistant microorganisms. They are the main cause of honey spoilage during storage. High yeast numbers cause rapid fermentation of honey. The rate of fermentation of honey is also related to the moisture content. 17% moisture is considered a safe level to inhibit yeast activity. On the other hand, the chance of crystallization increases as the moisture content decreases. The commercial standard yeast number is 500 cfu/mL or less.
Ultrasound is a non-thermal processing alternative to many liquid foods. Its mechanical power is used for gentle and effective microbial inactivation and particle size reduction. When the honey is exposed to ultrasound, most of the yeast cells are destroyed. Yeast cells that survive the action of sound waves often lose the ability to grow. This greatly reduces the speed of honey fermentation.
Ultrasound also eliminates existing crystals and inhibits further crystallization in honey. In this respect, it is comparable to heating honey. Ultrasound-assisted liquefaction can operate at approximately lower process temperatures. 35C, can reduce the liquefaction time to less than 30 seconds. Studies have shown that sonication at a frequency of 20 kHz can completely liquefy crystals in honey. The sonicated sample was maintained in the liquefied state for about 350 days (20% compared to heat treatment). Ultrasonic liquefaction allows for greater retention of aroma and flavor due to minimal heat exposure. The sonicated samples showed only a decrease in low HMF and a decrease in low amylase activity. The use of ultrasound helps to save processing costs compared to conventional heating and cooling due to the need for less thermal energy.