Evaluation of glucose and sucrose osmotic dehydrated and heat-air-dried Flordarking peach slices during conservation

Abstract

Prunus persica is a stone fruit source of multiple nutraceutical compounds. Fresh fruit has a short life; thus, many processing procedures have been used to increase its consumption in alternative forms. One strategy is the use of osmotic dehydration (OD) previous to conventional heat drying (D) since OD prevents browning, sugar caramelizing and degradation of bioactive compounds. Previously, we analyzed the effect on nutraceutical proprieties of an OD pre-treatment with glucose or sucrose solutions applied to peach slices. Here, we studied the stability along storage time of these slices kept under 50 % relative humidity (RH) atmosphere during 55 days. For this purpose, Flordaking peach fruits were harvested at commercial maturity. Fruits were washed, cut in slices, and immersed in CaCl2 and ascorbic acid solutions, to prevent browning. Slices were incubated at 40°C in a solution of sucrose or glucose (47° Brix) during 3 h under stirring. Next, slices were dried at 58°C during 4 h until 9.3-6.8 % relative water content and named as Suc+D or Glc+D, respectively. Slices were kept in a close jar where a supersaturated solution of sodium bromide was also placed inside to achieve a 55 % RH atmosphere. The vessel was maintained in a closed chamber in the dark at 25˚ C for 55 days. Samples were taken immediately after processing (0) and after 15, 33, 41 and 55 days. Surface color, fresh and dried weights were computed in each slice. To evaluate nutritional quality and bioactive compounds the following parameters were evaluated: total phenolic compounds (TPC), flavonoids, carotenoids, ascorbic acid, total soluble protein, glucose, sucrose and sorbitol contents and antioxidant activity by DPPH and ABTS methods, and expressed in a fresh or dry weight basis. A trained panel evaluated sensory texture of slices and texture was measured with texturometer. After 15 days of storage, water content of Suc+D and Glc+D slices raised until 25 % and kept constant during the period of analysis. While in Glc+D samples a decrease in carotenoids, total soluble proteins and antioxidant activity was found with the days of storage, no statistical differences were found in most of the parameters measured along 55 days. Similarly, in the case of Suc+D samples, the content of TPC, flavonoids, ascorbic acid, glucose, sucrose, sorbitol as well as the antioxidant activity remained unchanged during the period of conservation. Conversely, carotenoids and proteins decreased over time. Color analysis performed using a colorimeter revealed that during storage the color of slices slightly got reddish and less yellow than slices collected at day 0 when using sucrose or glucose for OD. Sensory descriptors and texture were similar in slices dehydrated with sucrose or glucose. In both cases, after 15 days firmness, oral breakdown and firmness decreased while texture, cohesiveness and crunchy perception increased. Collectively, our results show that an OD pretreatment with sucrose or glucose previous to conventional drying is effective to preserve the nutraceutical and nutritional components of the dehydrated peach slices during at least 55 days after processing, making a suitable product for consumption.