Sensory and nutritional attributes of Persian walnut kernel influenced by maturity stage, drying method, and cultivar

It is always a question whether sensory and nutritional properties of walnut are being affected by drying methods and harvesting date or not. In this study, effect of three drying methods (sun drying and drying at 20 and 30 degrees C) and four maturity stage (harvested weekly from 15 days after initiation of browning of packing tissue around the kernels until hull dehiscence) were tested on quality of two walnut cultivars ('Chandler' and 'Jamal'). Our results revealed that the walnut kernels dried at 20 degrees C have notably higher content of protein (13.1 gr/100 gr), saturated (palmitic [6.62%] and stearic acid [3.98%]) and polyunsaturated (linoleic [62%] and linolenic acid [14.59%]) fatty acids, higher walnut kernel color (85.33%) and lower walnut kernel shrivel (16.38%). Drying at 20 degrees C also caused the lowest peroxide value (0.33 meq/kg oil). Kernels of the Persian walnuts harvested later had a meaningful higher protein (14.49 gr/100 gr), oil (54.53%), saturated (9.37%) and unsaturated (96.36) fatty acid content, and lower shrivel index (13.46%) but with darker walnut kernel color (37.83%) and higher peroxide value (1.33 meq/kg oil) in comparison with the walnut kernels harvested earlier. Practical applications Nutritional and sensory quality of walnut kernel during postharvest life is determined by various factors. According to our results, from sensory and nutritional quality viewpoint, 'Chandler' is considered to be a more suitable cultivar than 'Jamal' and drying walnut kernels at 20 degrees C better preserved its sensory and nutritional quality than drying at 30 degrees C and sun drying method. Moreover, a positive correlation of walnut kernels color index and polyunsaturated fatty acid plus a negative correlation between shrivel index and nutraceutical properties of walnut kernels indicates that walnut kernel color and shrivel can simply reflect the nutritional quality of walnut kernels.

Automated summary

The study investigates the impact of drying methods and harvesting date on the sensory and nutritional properties of walnut kernels. It found that drying at 20 degrees Celsius resulted in higher protein and fatty acid content as well as better quality indicators compared to other drying methods. Additionally, late-harvested Persian walnuts showed higher protein and oil content but with darker color and higher peroxide value compared to early-harvested walnuts. The results suggest that walnut kernel color and shrivel can serve as indicators of the nutritional quality of walnut kernels.