The effects of preharvest treatments on the milling efficiency of red lentil

Abstract

ABSTRACT

Canada is currently the world leader in red lentil exports, a crop of significant economic importance to Western Canadian producers. It is important for the maintenance and growth of foreign markets that our growers are able to provide a consistent product. In the past few years, our exported red lentils have had variable quality, largely due variable weather conditions. A study was conducted to determine the effect of various preharvest treatments on the milling quality of our current red lentil cultivars. These cultivars, listed in order of increasing seed size, were CDC Robin, CDC Imperial CL, CDC Rosetown, CDC Blaze, CDC Impact CL, CDC Rouleau, CDC Redberry and CDC Red Rider. Replicated plots of each variety were grown in the summers of 2005 and 2006 at Floral, SK and Rouleau, SK. These were chosen with the intent of maximizing environmental differential between locations, especially in terms of soil texture and moisture availability. All locations were laid out using a randomized complete block design with four replicates. Replicated plots of each cultivar were subjected to preharvest treatments of desiccation with Diquat or swathing at early, recommended and late stages of maturity. The milling quality of the harvested lentils was determined for all treatment and cultivar combinations.

Before preharvest treatments were applied, each plot was assigned a maturity rating based on a 1 (immature) – 9 (very mature) scale. Plants exhibiting pods with a ‘buckskin’ colour and texture on the bottom third of the plant were considered to be at early maturity and assigned a rating of 3. Similarly, when pods of buckskin colour and texture were found in the middle third of the plant, a maturity rating of 6 was assigned while a value of 9 would be assessed when the entire plant had all brown, rattling pods except for a small portion of buckskin pods in the top third of the canopy.

Based on this 1-9 scale, a total of six different harvest treatments were carried out: swathing or chemical desiccation at early, intermediate or late stages of maturity. Swathed plots were cut using a gas-powered sickle-mower, then covered with bird mesh which was staked to the ground until harvest to prevent wind damage. Desiccated plots were sprayed with Reglone ™ (diquat) using a CO2-pressurized backpack sprayer. They were left standing until harvest. Following mechanical harvest, seed from each plot was placed in mesh bags and forced-air-dried to approximately 13% moisture, then placed in a controlled storage chamber held at 5oC.

Seed samples of two complete sets of replicated treatments were cleaned, then sized by passing them over round, then slotted sieves using the ‘forty-shakes’ method. The two most frequent seed diameter and thickness fractions from each plot were set aside for milling. Samples were hydrated to 12.5% moisture which is the ideal moisture content for high milling quality according to research conducted by Dr. Ning Wang at the Grain Research Laboratory in Winnipeg, MB. The samples were then milled using either a Satake or a Turkish table top pulse dehuller. Following milling, samples were passed through a Carter dockage tester (Simon-Day Ltd., Winnipeg, MB) to separate whole and split seeds from broken or damaged seeds and hull material. Each sample was assessed for: 1) milling efficiency (percent split and unsplit cotyledons recovered from the total sample); 2) football recovery (percent dehulled lentils with unsplit cotyledons); and 3) dehulling efficiency (percent of cotyledons with over 98% of the seed coat removed. Dehulling efficiency values were assessed using a DuPont AcurumTM seed scanner (DuPont Canada, Toronto, ON).

Under favorable harvest conditions, preharvest treatments had no effect on milling efficiency, percent football recovery or dehulling efficiency. However, plots subjected to cool, wet harvest conditions produced lentil samples of highly variable milling quality. Early desiccation significantly reduced milling efficiency to below 70%, whereas early swathing resulted in milling efficiency above 85%. CDC Robin and CDC Imperial CL had the highest milling efficiencies. Similarly, cool wet harvest conditions caused percent football recovery to drop from approximately 80% to around 50%. Early swathing was the most effective for producing footballs, with smaller-seeded varieties producing the most. Cool, wet harvest caused dehulling efficiency to drop from the 97.3 – 99.9% range to 91.5 – 98.7%. Early desiccation had the most negative effect on dehulling efficiency, whereas early swathing produced the highest values. Under these conditions, smaller-seeded varieties had the lowest dehulling efficiencies.

The results of this study will be valuable for developing agronomic practices specific to red lentil and for improving the quality of Canada’s exported product.