Effects of ultrasonic pretreatments on quality, energy consumption and sterilization of barley grass in freeze drying

Barley grass is a plant resource for rehabilitation therapy. Its processing requires retaining nutrition well for rehabilitation cure of consumers. To meet the aim as well as low energy consumption and microbiological safety of products, ultrasonic treatments (UT) were applied to bathing materials at different power levels (10, 30, 45, 60 W/L) for 10 mins. After treatments, the bathed barley grass (100 g) was freeze-dried under vacuum −0.09 MPa with fixed power of 2 W/g. Parameters of color, microbial colony, energy consumption, glass transition temperature, moisture content, water activity, taste substances, contents of flavonoid and chlorophyll were determined after drying. In contrast with no treatment case, UT (45 W/L) decreased drying time by 14% and decreased energy consumption by 19%; UT (60 W/L) decreased total microbial colonies by 33%. Also, UT (30 W/L) yielded contents of flavonoid (9.2/kg) and chlorophyll (10.5 g/kg) of dried sample; UT power (10 W/L) yielded the highest L∗(51.5) and the lowest a∗(−9.3) value. Simultaneously, UT leads to a higher glass transition temperature (Tg), lower water activity and produces less sourness and bitterness of dried products. Ultra-sonication is an alternative to improve quality, flavor and energy consumption of barley grass in freeze drying.