The effect of osmotic dehydration on the polyphenols content in onion

Abstract

Background. The onion is one of the most popular vegetables in the world, often used in the food industry. The purpose of this work was to determine the effect of osmotic dehydration of onions after storage in solutions containing various amounts of sucrose and sodium chloride on the course of osmoconcentration and the level of polyphenols in the dehydrated vegetables. The results could be useful to define the dehydration conditions under which a product retains the highest content of these health-promoting substances. Materials and methods. Onions var. Robusta were used. The vegetables were stored for six months at 0°C (air relative humidity 75-80%). They were cut into quarters just before dewatering. Samples of 20 ±1 g were dehydrated for five hours in a 40-60°Bx sucrose solution and a 5-15% NaCl solution (25°C); the weight ratio of the sample to the solution was 1:5. The contents of polyphenols and dry matter were determined. Results. The use of a mixture of two osmotic agents (sucrose, sodium chloride) was more effective in the increase of dry matter content than using only sucrose. Nearly 49% dry matter content in onion was obtained by using a 60% solution (50% sucrose + 10% NaCl) for five hours. The greatest differences in the content of total polyphenols occurred during the first hour. After this time, retention amounted to 48-90%, depending on the concentration of sucrose (40-60%) and sodium chloride (5-15%). The retention of diglycosides of quercetin (mainly quercetin-3,4'-diglucoside) was lower than that of monoglycosides (mainly quercetin-4'-glucoside). Following dehydration in a solution containing 60% sucrose and 10% NaCl, after three hours, there was about one third of the initial amount of the above-mentioned compounds in onion. Conclusion. The increase in the concentration of the hypertonic solution, being a mixture of sucrose and sodium chloride, causes a reduction in the retention of total polyphenols in osmotically dehydrated onions. The smallest losses occur after applying a 40% sucrose solution with NaCl up to 10%.

Application of heat pump drying technology to produce dried mango products from Tu Quy mango (Mangifera india L.), Vietnam, on a pilot scale

“…Furthermore, the migration of water from mango slices to the syrup medium also carried polyphenol compounds. Thus, increasing the total solute concentration decreased TPC, which was consistent with the report by Grzelak-Błaszczyk et al (2020). The permeation samples at 25°Bx and 30°Bx produce the highest TPC value.…”

Mango enriched with sucrose and isomaltulose (Palatinose®) by osmotic dehydration: Effect of temperature and solute concentration through the application of multilevel statistical models

“…The OD time (300 min) was chosen based on preliminary tests that showed that the osmotic equilibrium was reached at that time period. Other authors also used similar time periods (Grzelak‐Blaszczyk et al, 2020; Junqueira et al, 2018; Prithani & Dash, 2020).…”