Effect of active edible coating on quality properties of green-raisin and ranking the samples using fuzzy approach

The present study investigated the effect of monoglycerol-stearate and carnauba wax (0.5% w/v) containing Shirazi thyme essential oil (TEO: 150 ppm) on the physical (moisture content, water activity, firmness and color), microbial (total counts, yeast and mold) and sensory properties of raisin during 12 weeks storage at room-temperature. Sensory quality of samples was investigated by the fuzzy-ranking method. The results show that there was a significant difference in moisture content and water activity between uncoated and coated samples (p < 0.05). A negative and powerful correlation (R = − 0.927) was found between moisture content and firmness based on Pearson's correlation coefficient. The lipid-based coating, especially without TEO, show better textural quality (p < 0.05). The ΔE value of non-coated samples was significantly higher than lipid-based coated samples without TEO (p < 0.05). Thymol (42.13%), carvacrol (14.88%) and p-cymene (11.31%) are the major constituents of TEO. At the end of storage, the lowest total counts and yeasts and molds was recorded for samples coated with TEO (2.3 and 1.6 Log CFU/g). The results of the fuzzy ranking showed none of the sensory attributes were considered the “unimportant” by the panelist. The taste and texture were the most important sensory properties, while color was the weakest. The results of fuzzy ranking introduced the carnauba wax coating without TEO as the best treatment. Overall, lipid-based coatings effectively can be used as ecofriendly and economic edible coating to improve quality and the shelf-life of raisins. However, the use of essential oils that are more harmonious with raisins can be recommended.