Studies on Processing and Storage of Walnuts (Juglans regia L )

The present investigations on processing and storage of walnuts were carried out at Food Processing and Training Centre, Division of Post Harvest Technology, SKUAST-K, Shalimar during 2007 to 2009. Green walnuts were subjected to different concentrations of ethephon for various dip and holdimg durations for enhancement of hull dehiscence and shell appearance. In addition, whole walnuts and walnut kernels were dried using different drying techniques, and kernels pretreated with various antioxidants were packed in different packaging materials to monitor the changes in various quality attributes during 18o days of ambient storage. Post harvest application of ethephon significantly increased the hull dehiscence compared to control (water dip) and maximum dehiscence of 93.87 per cent was recorded in samples subjected to ethephon (@ 3000 ppm) for dip duration of 24 hours and holding duration of 9 days. Bleaching of whole walnuts in acidified sodium chlorite significantly improved shell colour and best colour scores were achieved in samples dipped in 1.0 per cent concentration solution for 6 minutes. Shell colour decreased significantly from 3.40 to 3.13 values during 180 days of storage but showed no deterioration upto 45 days of storage. Drying of whole walnut from an initial moisture content (db) of 81.98 per cent to final moisture of 11.74 and 12.38 per cent was achieved in 36 and 23 hours in sun- and solar tunnel drying, respectively, while as in mechanical drying at (40 and 45oC) it took 21 and 18 hours, respectively. In case of kernel drying, the final moisture content (db) of about 5 per cent from an initial content of 37.93 per cent was achieved in 18, 14, 13 and 9 hours in that order. Drying methods exhibited non-significant effect on the moisture content of the whole walnut, while as their packaging in polyethylene resulted in significantly lowest moisture content compared glass or PET packaging throughout storage. Mechanically (40oC) dried and glass packaged whole walnuts proved significantly superior by exhibiting highest crude fat content (59.82%), maximum iodine value (145.72) and minimum peroxide value (3.17) compared to rest of treatment combinations throughout storage. Mechanical drying of whole walnuts and their packaging in glass proved significantly superior in maintaining shell colour as well as colour, taste and texture of kernels compared to rest of the treatment combinations; but after 45 to 180 days of storage, there was a gradual decline in these attributes irrespective of treatments. Application of antioxidants showed a non-significant influence on moisture content of kernels. Vacuum packaged kernels recorded significantly higher moisture content (4.08%) compared to cellophane packed samples (3.81%). Application of BHT+BHA (0.015% each) to kernels and their packaging in vacuum packaging proved more effective in maintaining higher fat content, higher iodine value and lower peroxide value compared to rest of the treatments. However, there was a gradual decrease in fat content and iodine value, and increase in peroxide value with increase in storage period. Furthermore, colour, taste and texture of kernels was significantly influenced by antioxidants, packaging materials and storage periods except that antioxidants exclusively did not show any significant effect on texture. Application of BHT+BHA (0.015% each) treatment as well as vacuum packaging of kernels proved most effective by exhibiting maximum colour, taste and texture values than that of BHT (0.03%) or BHA (0.03%) treatments and cellophane packaging upto 180 days of ambient storage