# Effect of Lentinan on Lipid Oxidation and Quality Change in Goose Meathalls during Cold Storage
## 3 Results and Discussion  
### pH and Color  
pH value is an important indicator to measure meat quality because it directly affects protein stability and protein functionalities [27]. The LNT content (_p_ < 0.001), storage time (_p_ < 0.001) and LNT content \(\times\) storage time (_p_ < 0.001) significantly influenced the pH in the tested goose meatball (Table S1). As Table 1 shows, the pH value increased first (from day 3 to day 7) and then decreased (from day 7 to day 12) during the storage time. The initial increase in pH may be due to the action of microorganisms and endogenous enzymes that promote the decomposition of meat protein to produce alkaline substances [28]. However, microbial metabolism, such as that of lactic acid bacteria, produces more acid, resulting in a decrease in pH of goose meatballs afterwards [19]. On the other hand, with the increase in LNT content during cold storage, the pH of goose meatballs generally showed a decreasing trend. The pH was significantly reduced even at 0.5% level of LNT stored for 3 days compared to the sample without LNT, and the pH of 4% LNT group dropped the most from 6.073 to 5.930, which may be owing to the acidic nature of LNT. In addition, it is also possible that the presence of LNT inhibited the growth of microorganisms, thus reduced the production of alkaline substances, resulting in the decrease in pH value. However,there was no significant difference among the pH of LNT samples stored for 12 days where the pH tended to be stabilized. Color is an important indicator to judge food quality [29]. The effects of LNT content and storage time on color changes in goose meatballs during cold storage (4 \({}^{\circ}\)C) are shown in Table 1. For meat products, the most important and intuitive parameter in color is the L* and a* values, because it is often associated with consumers' acceptance of meat color [30]. The L* value of the samples stored for 12 days significantly decreased compared to the samples with 3 and 7 days of storage. And, with the extension of storage days (from 3 days to 12 days), the a* value of goose meatballs generally showed a decreasing trend, however, when the addition of LNT was 0.5%, 1% and 2%, the a* of the samples did not show significant difference. It is understood that proteins and lipids undergo oxidation and degradation during storage, resulting in structural changes that alter the absorption and scattering of light in goose meatballs [31]. In addition, oxidation products such as hydrogen peroxide, ketones, acids, and aldehydes also affect color [32]. With the increase in LNT concentration, L* value showed a downward trend during the whole storage period, which may be the fact that LNT is a brown powder that dispersed in the goose meatballs during production process, therefore excessive addition of LNT caused a decrease in the L* value of sample. However, the a* value showed an increasing trend with the increase in LNT content during storage, specifically, compared with the samples without LNT, the a* of the 4%LNT group increased by 28.15%, 48.50% and 100.03%, respectively, during storage for 3, 7 and 12 days, which indicated that LNT could inhibit the oxidation of fat. LNT has antioxidant activity and can effectively prevent myoglobin from oxidizing to high-valent iron myoglobin [33]. In addition, the increase in LNT concentration had little effect on the b* value of the samples compared to the samples without LNT addition. However, there was significant interaction effect of the LNT content \(\times\) storage time for b* of the tested sample (\(p<0.001\)) (Table S1). Total color difference (\(\Delta\)E) is a common method to show the magnitude of position difference in CIE LAB color systems and the higher \(\Delta\)E, the greater the relative change in color and the paler the color than the control [20]. With the increase in LNT content, \(\Delta\)E showed a rising trend during the whole cold storage period, indicating that adding LNT could change the total color of goose meatballs.