## 3 Results and Discussion
### Chicken Meat Preservation with Kidney Bean Protein Hydrolysates  
#### 3.2.1 Physicochemical Changes during Cold Storage  
Table 7 presents the changes in some physicochemical parameters of raw chicken meat during cold storage for 30 days, i.e., pH, metmyoglobin (%), TVBN (mg N/100 g), and lipid oxidation inhibition (%), in response to graded additions of BKH, RKH and WKH. All parameters significantly increased with increasing the storage period from 0 to 10, 20, and 30 days, but lipid oxidation inhibition (%) significantly decreased. The pH values, metmyoglobin, and TVBN significantly decreased with the increments of BKH, RKH, and WKH concentrations (200, 400, and 800 ug/g) in a concentration-dependent manner. The pH value of the control sample increased from 5.6 to 8.9, i.e., reflecting a 40% relative increase after 30 days of cold storage. Supplementing meat with protein hydrolysate (800 ug/g) decreased pH by 25-30% of the control value after 30-day cold storage. The increase in the pH value with storage time (30 days) in the control samples coincided with parallel increases in total volatile basic nitrogen (TVBN), i.e., from 6.5 mg N/100 g at zero time to 8.35 mg N/100 g after 30 days of cold storage. This pH increase is probably a result of the metabolic activities of the contaminating spoilage bacteria, which can hydrolyze the proteins and lipids producing NH3 [86]. Treating the stored meat with the protein hydrolysate significantly reduced this value in a concentration-dependent manner, specially BKH (800 ug/g), which maintained the level of TVBN down to 6.50 mg N/100 g after 30 days of cold storage. This action is apparently due to the antibacterial activity of the protein hydrolysate previously evidenced. Similar results were observed by [PERSON], et al. [21], who reported that minced beef supplementation with pepsin kidney bean hydrolysate (100, and 200 ug/g) reduced the pH increase by 10%. The level of Met-myoglobin in the control sample increased rapidly with storage reaching 52.5% after 30 days of cold storage, i.e., exceeding the acceptable level in meat (40%). The addition of protein hydrolysates (800 ug/g) to chicken meat significantly slowed down the rate of meat deterioration, keeping the level of metmyoglobin down to 22-28 % after 30 days storage, i.e., achieving relative reductions of about 58-47 % of the control value, respectively. The highest reduction (58%) was achieved by BKH (800 ug/g). The increase in metmyoglobin with storage is evidently due to the auto-oxidation of meat protein and the oxidation of myoglobin to met-myoglobin, leading to undesirable meat color [87]. The reduction of this value by hydrolysate addition is probably due to their antioxidant action, previously quantified (Figure 3). Finally, the addition of protein hydrolysates to chicken meat at a high level (800 ug/g) significantly increased the efficiency of inhibiting lipid oxidation by about 59-70% over the control. The addition of protein hydrolysate to the preserved meat significantly inhibited the unwanted oxidative changes because of antioxidant activity, previously mentioned. Lipid oxidation is the main factor affecting the meat's lifetime during storage. The formation of hydroperoxides and aldehydes are indicators of lipid oxidation [88]. [PERSON], et al. [89] found the addition of phaseolin isolated from red kidney bean to zebrafish inhibited the lipid oxidation by 82%, and [PERSON], et al. [90] found that the addition of fish protein hydrolysate to chicken meat breast during storage delayed the lipid oxidation and all unwanted changes.