PROTEIN-QUALITY AND ENERGY DENSITY OF GREEN PEAS AS INFLUENCED BY SEED SIZE AND TIME OF HARVEST

Green peas (Pisum sativum L) were harvested at three different time po ints-3 days apart-and subsequently sorted into four fractions accordin g to seed size (diameter > 10.2 mm; 10.2-8.75 mm; 8.75-8.2 mm and 8.2- 6.0 mm). Three varieties from two years were investigated. The study c omprised a total of 31 green pea samples. The average protein content of the samples was 276 g kg(-1) DM with relatively low variation (SE = 5.7). Protein content was highest in the smallest seeds. The average energy content was 18.6 MJ kg(-1) DM. Dietary fibre content was 226 g kg(-1) DM, the major part (77%) as insoluble fibre. Seeds of early har vest and seeds with the smallest diameter had the lowest fibre ODF and TDF) content and at the same time the highest energy digestibility. T he average energy digestibility was 83.2%. Protein digestibility was r elatively high (average 92.1%), while biological value (BV) and net pr otein utilisation (NPU) were moderate to low (60.6% and 55.8% respecti vely) due to low contents of the essential amino acids (g per 16 g N), especially tryptophan, methionine + cystine and lysine. Contents of l ysine, tryptophan and methionine + cystine were more than 20% higher i n the smallest seeds compared to the larger seeds. Similar differences were observed in seeds of late harvest as compared with seeds of earl y harvest. Correlation coefficients revealed a strong positive correla tion between lysine, tryptophan and methionine + cystine content and t he biological value of green pea protein. The three varieties investig ated showed no differences in the chemical parameters although small d ifferences in BV and NPU were observed.