FREEZE DRYING WITH OSMOTIC PRETREATMENT AS A METHOD FOR PRESERVATION OF LONGKONG (Lansium Parasiticum THICK-SKINNED CULTIVAR) FRUIT
Keywords:
Longkong, freeze drying, osmotic dehydration, nutritional valueAbstract
In southern provinces of Thailand, when seasonal yield of longkong outpaces market demand its price sinks suddenly and directly affects farmers. Therefore, the objective of the study was focused on developing dried longkong using osmotic dehydration as a pre-treatment followed by freeze-drying to prolong the shelf life of longkong. The effects of the concentration (1, 2, 3, and 4% w/v) and type (calcium chloride and calcium lactate) of firming agent on the firmness were studied. The effect of the concentrations (30, 40, and 50°Brix) and soaking times (24 and 48 h) of sucrose solution on customers’ satisfaction were also investigated. The nutritional values of the freeze-dried products were analyzed and their shelf life in aluminum foiled bags and PET bottles were investigated at room temperature (25-30°C) for 24 weeks. The results showed that peeled longkong immersed in 1% (w/v) calcium chloride solution had the highest firmness of 35.430±5.521 g. Sensory characteristics of the finished product were evaluated and the results revealed that soaking longkong in sucrose solution of 30°Brix for 24 h represented the most satisfying qualities and overall consumer liking. Study of the product shelf life showed that dried longkong packed in both aluminum foil bags and plastic bottles (PET) could be kept at room temperature for 24 weeks. Microbiological qualities including total bacterial count, Salmonella spp., Staphylococcus aureus, Escherichia coli, as well as yeast and mold count were tested; negative results were obtained for these tests and the standards according to TIS 919-2532 were met. It can be concluded that freeze-drying with osmotic pretreatment can be efficiently used as a method to prolong the shelf life of fresh longkong fruit and create a product with satisfactory qualities.
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