Honey is in great demand as a food and medicine. Ultrasonic treatment is an effective means of destroying undesirable components such as crystals and yeast cells in honey. As a non-thermal processing technology, it reduces the content of hydroxymethylfurfural and better preserves amylase, aroma and flavor.
background
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.
Enzyme
Honey contains starch digestive enzymes. Amylase is sensitive to heat and easily inactivated, so amylase activity is an important quality indicator for 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 to 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.
Yeast and microorganism
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.
crystallization
Honey crystallizes naturally because it is a supersaturated sugar solution with a sugar content of more than 70% and a relative water content of about 18%. When glucose becomes a more stable glucose monohydrate saturated state, glucose spontaneously precipitates from supersaturation by losing water. This results in the formation of two phases - the liquid phase above and the solid crystal below. These crystals form a crystal lattice in which the other components of the honey are fixed in a suspension to form a semi-solid state. Crystallization or granulation is undesirable because it is a serious problem in the processing and sale of honey. In addition, crystallization limits the flow of untreated honey from the storage container.
Heat treatment
After being extracted and filtered, the honey is heat treated to reduce moisture levels and destroy the yeast. Heating does help to crystallize the crystals in the honey. Although heat treatment can effectively reduce water loss, reduce and delay crystallization, and completely destroy yeast cells, it can also cause product deterioration. Heating significantly increased the level of hydroxymethylfurfural (HMF). The maximum allowable legal level for HMF is 40 mg/kg. In addition, heating reduces the activity of the enzyme (eg, amylase), affects sensory quality and reduces the freshness of the honey. Heat treatment also darkens the natural honey color (browning). In particular, heating above 90 °C results in caramelization of the sugar. Heat treatment also does not completely eliminate heat-resistant microorganisms.