The prevention of browning during drying by the cold dipping treatment of sultana grapes

Abstract

The activity of an active polyphcnol oxidasc which is mainly located in the skin of sultana grapes decreases during ripening, but it is still active a t full maturity. It is suggested that the browning of untreated grapes during drying is mainly caused by this enzyme. The dipping process, used to increase the drying rate, prevents browning, but i t does not affect the enzyme or its activity directly. The drying rate is increased without a corresponding increase in oxygen uptake of the fruit, so that it is concluded that the enzyme is unspecifically inhibited by rising sugar concentrations, and not by components of the dipping solution. The prevention of browning of drying grapes can be achieved by an increased drying rate without dipping treatment.-4 mutant ' Bruce's Sport ' of the grape variety Thompson's seedless, which yields light-coloured raisins, does not contain an active polyphenol oxidase, but contains similar amounts of phenols.

Effect of ethyl oleate on drying characteristics of mulberries

“…Dipping waxy fruits for several seconds in a solution of ethyl oleate or other suitable compounds (usually fatty acid derivatives used as wetting agents and emulsifiers) greatly reduces the drying time [9][10][11]. Fatty acid esters are applied to the surface of the fruit by dipping, resulting in a coating which apparently breaks down the waxy cuticular fruit surface, resulting in a reduced resistance to moisture loss.…”

Browning reactions during storage of low-moisture Australian sultanas: Evidence for arginine-mediated Maillard reactions

“…Drying sultana grapes Most dried Sultana grapes (sultanas) produced in Australia are subjected to an alkaline 'cold-dip' following harvest to accelerate drying and thus produce light-golden coloured sultanas as dried fruit (Fogerty and Burton 1981, Grncarevic and Lewis 1976, Grncarevic and Hawker 1971, Ramshaw and Hardy 1969, Radler 1964, Grncarevic 1963). The 'cold dip' process is critical to this outcome.…”

“…PPO browning Browning in sultanas is thought to occur via two distinct processes; one enzymatic, the other non-enzymatic. Enzymatic browning occurs when the grape enzyme polyphenoloxidase (PPO) comes into contact with endogenous grape phenolics compounds during grape drying (Rathjen and Robinson 1992a, 1992b, Macheix et al 1991, Singleton et al 1985, Singleton et al 1984and Radler 1964. In healthy grape tissue, PPO is separated from the main grape phenolic substrate trans-caftaric acid (trans-caffeoyl tartaric acid), but with any loss of that compartmentalisation occasioned by physical damage, including berry shrinkage, the enzyme comes in contact with the substrate and browning occurs (Cheynier and Moutounet 1992, Cheynier et al 1990, Moskowitz and Hrazdina 1981.…”

Drying Kinetic Studies on Single Layer Thompson Seedless Grapes Under Controlled Heated Air Conditions

“…A chemical pretreatment (hot or cold) is generally applied to decrease the skin resistance and hence improving moisture diffusion through waxy cuticle (Ponting and Mcbean 1970). The hot dip pretreatment reduces the drying time significantly while cold dip pretreatment produces raisins of an attractive golden brown color without producing cracks on the grape berries (Radler 1964).…”