جستجوی مقالات مرتبط با کلیدواژه "سیب زرد لبنانی" در نشریات گروه "صنایع غذایی"

Osmotic dehydration involves the partial removal of water by direct contact of a product with a hypertonic medium such as high concentration of sugar, salt or sugar-salt solutions. In this process, food pieces are immersed in a hypertonic solution. The natural membrane of food cells acts as a semipermeable layer so the water moves across the membrane from an area of high water potential (low solute concentration) to an area of low water potential (high solute concentration), meaning the driving force for water removal is the concentration gradient between the solution and the intracellular fluid. During osmotic dehydration, osmotic solute is absorbed by food materials and has undesirable effects on water removal, nutritional and organoleptic properties. Use of coating improves the osmotic processing. Best factor for evaluation of coating material is performance ratio (WL/SG). So a coating should reduce solid uptake without negative effects on water removal.
The apples (Golden delicious) used in this study were purchased from a local market in Mashhad (Iran) and stored at 4-6°C before processing. The sucrose (99.9%, Fariman sugar company, Iran), carrageenan (kappa type, Negin Khorak Pars Company, Iran), carboxy methyl cellulose (sandros, Japan) and calcium chloride (Dr. Mojallali Lab., Iran) were also used. In this work, apple cubes were single and double coated in three concentrations (0.5, 1 and 1.5% w/w) of carboxy methyl cellulose (CMC) and carrageenan solution and dehydrated osmotically in different concentrations (30, 45 and 60˚ BX) of sucrose solutions.
The results of this study indicated that increasing coating solution concentration from 0.5% to 1.5% decreased water loss. Also the water loss increased when the number of coating layers and the concentration of osmotic solution increased (from 30 to 60 ˚ BX). Generally, water loss and solids uptake in the samples coated with carrageenan was higher and lower than their CMC counterparts, respectively. The solids uptake in the samples coated with CMC increased by increasing the number of layers, osmotic solution concentration (from 30 to 60˚BX) and coating solution concentration (from 0.5 to 1.5%). The solids uptake increased and decreased with increase in layer number and coating solution concentration (from 0.5% to 1.5%), respectively. Increasing the osmotic solution concentration up to 45 ˚ BX increased solids uptake but, more increasingly did not have a significant effect on it. Finally, it cannot be said strictly that one coating type would facilitate osmotic process or not. It depends on various process factors. Among the 36 treatments studied in this research, the single coated samples with 1% carrageenan treated in 60 ˚ BX sucrose solution and the single and double coated samples with 0.5% CMC treated in 45 ˚ BX sucrose solution were the best, as they had 50% higher performance ratio than control (uncoated) sample.

Use of coating treatment prior to osmotic dehydration can improve process performance by reducing solids uptake. In this study, the effect of coating-osmotic treatment on drying of apple cubes was investigated. So, the apple cubes (1 cm3) were coated in two concentrations (1 and 1.5% w/w) of carboxy methyl cellulose (CMC) and carrageenan solutions and osmotically dehydrated in different sucrose solution concentrations of 45 and 60˚ BX, for 150 minute. Then, coated apple cubes were dried in a hot-air drier at 70˚C to final moisture content of 20% (w.b) and the rehydration ratio of dried samples was measured. Our results revealed that the highest performance ratio was related to single-coated apple cubes with 1% solution of carrageenan, osmo-dehydrated in 60˚ BX and single and double-coated samples with 0.5% solution of CMC, osmo-dehydrated in 45˚ BX. Investigation of final drying showed that coated materials created a strong barrier against water removal and decreased the drying rate. Dried coating layers on apple cubes also prevented the samples from water absorption, and the coated apple cubes had a lower rehydration ratio than noncoated ones. We found that coating is effective only during osmotic process and it is not a good and efficient method for the final air drying.

Apple samples (Golden delicious variety) were harvested at 5 different times at one-week intervals from September 17 to October 15. To evaluate the texture changes during three months storage in a cold room at 0 C and 95% RH، chemical and textural analyses were carried out. In chemical analysis، acidity، soluble solids (Brix)، total sugar and reducing sugar were determined. The samples were cut into two halves and texture analysis was performed on the halves in the form of “with and without skin”. Force-deformation curves were obtained by carrying out uniaxial penetration and compression tests. Crispness، fracturability of the skin and hardness of the flesh، total firmness، toughness and modulus of elasticity were calculated and compared using the curves. The results showed that during the storage time، acidity decreased and Brix، total sugar and reducing sugar increased. The mechanical properties were decreased by increasing storage time. The smallest changes on the fracturability of the skin and hardness of the flesh and modulus of elasticity were generally observed for samples harvested before full maturation.