Degradation of higher fatty acids in perennial ryegrass and white clover following drying and storage

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Abstract
Bulk samples of perennial ryegrass and white clover were deep frozen immediately after harvesting. Within 2 days one portion was freeze‐dried, one was oven dried at 108 ºC, and the remainder was stored intact at −16 ºC. The two dried samples, after grinding, were stored either in air at ambient temperature, or under nitrogen at −16 ºC. Portions of the deep‐frozen, intact sample were withdrawn after storage for 2, 4 1/2 and 9 months, freeze dried and ground, immediately prior to analysis. Determinations of the total higher fatty acids (HFA) by titration and individual higher fatty acids by gas‐liquid chromatography, were made on all samples after storage for the above periods.HFA in the dried and ground ryegrass or clover fluctuated throughout the experimental period under all conditions of storage. The greatest deterioration was exhibited by freeze‐dried, air‐stored ryegrass which lost linolenic acid at a rate of 0.55 mmol 100 g−1 month−1. Negligible changes in total nitrogen occurred in all dried samples after 9 months storage. Non‐protein nitrogen extracted from clover, however, was significantly higher after oven‐drying as compared with freeze‐drying.The most satisfactory mode of storage was to store the intact, undried herbage at −16 ºC and then freeze dry and grind immediately before analysis. Under these conditions, HFA changed little over 2 months.

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