Effects of post-harvest processes including pre-conditioning, drying and rewetting cycles and storage period on dehulling and cooking quality characteristics of red lentils

Abstract

Red lentil (Lens culinaris Medikus), an important pulse crop produced in Western Canada, is mainly consumed as split or whole cotyledon (“football”) after the seed coat has been removed through dehulling. However, related information on the effects of storage time, postharvest treatments and storage temperature on the dehulling efficiency and cooking quality of red lentils at different moisture contents are not readily available for processors, marketers, breeders, as well as growers. The objective of this study is therefore to investigate the effect of storage temperature, postharvest treatments and storage time on the dehulling efficiency and cooking quality of red lentil. While a laboratory Satake dehuller was used to evaluate the dehulling characteristics of red lentil, an automated Mattson cooker was used to determine the cooking quality. Red lentil of ‘Robin’ variety for 2007 harvest with moisture contents of 10.07%, 11.31% and 13.27% w.b., as well as ‘Robin’ samples for 2008 harvest of moisture contents 10.13%, 11.52% and 13.37% were kept in storage at two temperatures of 5oC and 25oC. In addition, samples with the moisture contents of 10.07%, 10.13%, 13.27% and 13.37% were subjected to three freeze-thaw cycles and stored at 5oC only. Similar treatments were given to lentil samples of ‘Impact’ variety with moisture contents of 10.21%, 11.56%, and 13.14% w.b. for 2007 harvest and 10.33%, 11.48% and 13.54% for 2008 harvest. In addition, lentil sample of ‘Impact’ and ‘Robin’ varieties at 13.14% and 13.27% (w.b.) moisture contents for 2007 harvest as well as 13.54% and 13.37% moisture contents for 2008 harvest respectively were further reconditioned to a moisture content of 18% (w.b.). As part of the postharvest treatment, these samples were dried at near ambient temperature and at 80°C under forced convention (simulating extreme drying conditions) to two final moisture contents of 10% and 13%. These samples were further stored at 5°C and 25°C. Dehulling efficiency and cooking quality were determined after 1 and 6 month storage. Also, lentil sample (2007 harvest) of ‘Impact’ variety at 10.21% and 13.14% as well as ‘Robin’ variety at 10.07% and 13.27% moisture contents were subjected to 5 cycles of drying and rewetting in the range of ±2% from its nominal moisture and tested for quality (dehulling efficiency and cooking quality) after 1 and 2 months storage at 5°C. This same postharvest treatment was given to lentil sample (2008 harvest) of ‘Impact’ variety at 10.33% and 13.54% moisture contents as well as ‘Robin’ variety at 10.13% and 13.37% moisture contents. Tests on dehulling efficiency and cooking quality were conducted at specific time intervals. Generally, there was a decrease in the dehulling efficiency values of ‘Robin’ and ‘Impact’ lentil samples with storage time up to 12 months for both harvest years (2007 and 2008). Among the postharvest treatments considered in this study, the drying and rewetting of lentil samples (‘Robin’ and ‘Impact’) had the most significant impact on dehulling efficiency. For other postharvest treatments, the trends were not consistent. In some cases dehulling efficiency increased for samples dried at 80°C, but observations like this were not consistent for other variety. Generally, storage time did not affect the cooking time values of ‘Robin’ and ‘Impact’ lentil samples. This is true for samples stored at 5°C, 25°C and 5°C subject to freeze thaw cycles, and also those subjected to other postharvest treatments at different moisture contents. Drying and rewetting of ‘Robin’ and ‘Impact’ lentils significantly increased the cooking time of these samples.