Heating Has No Effect on the Net Protein Utilisation from Egg Whites in Rats.

Ryosuke Matsuoka,Yayoi Takahashi,Mamoru Kimura,Yasunobu Masuda,Masaaki Kunou

doi:10.1155/2017/6817196

Abstract

Egg whites (EW) are a good source of protein; however, they are typically heated prior to consumption. Therefore, we investigated the effects of different heating conditions on the protein utilisation rate of EW. Male Sprague-Dawley rats (n = 36, 198 ± 1 g) were divided into six groups and fed American Institute of Nutrition-76 chow containing unheated EW, soft-boiled EW, boiled EW, milk whey protein, soybean protein, or no protein over a 10-day period using pair-feeding. Urine and faeces were sampled daily beginning on day 5 to measure nitrogen content and the net protein utilisation (NPU) rate. The soybean protein group had a significantly lower level of food intake and was thus excluded from subsequent analyses. The NPU value was similar among the unheated, soft-boiled, and boiled EW groups (97.5 ± 0.4, 96.5 ± 0.1, and 96.5 ± 0.7, resp.). The EW group values were significantly higher than the whey group values (90.5 ± 1.0). These results show that EW serve as a good source of protein, irrespective of heating.

Highlights

Chicken eggs are highly nutritious and contain most recommended nutrients, except vitamin C and dietary fibre
egg whites (EW) are a good source of protein, as evidenced by their amino acid score of 100 and high rate of net protein utilisation (NPU) [1, 10]
A previous study reported that unheated EW contain protease inhibitors, which can inhibit the activity of trypsin, elastase and chymotrypsin [11]

Summary

Introduction

Chicken eggs are highly nutritious and contain most recommended nutrients, except vitamin C and dietary fibre. A previous study reported that unheated EW contain protease inhibitors, which can inhibit the activity of trypsin, elastase and chymotrypsin [11]. EW increased trypsin and chymotrypsin activity to a greater degree than egg yolks or whole eggs; the function of protease inhibitors in EW is not fully understood [12]. Heated EW are thought to inhibit protease inhibitor activity and increase protein absorption. It has been reported that chymotrypsin activity is inhibited to a greater degree in heated whole eggs, suggesting that protein absorption and NPU are greater in unheated eggs [12]. We investigate the effect of different heating conditions on the NPU of EW and compare these data with the widely used sources of protein: milk whey and soy

Methods

Results

Conclusion