Effect Of Treatments With Cysteine On Storage Of Fresh-cut Cistanchesherba Ⅱ

2 Results and analysis

2.1 Effect of cysteine treatment on the color of fresh-cut Cistanche deserticola. 

Color is one of the most intuitive indicators reflecting the aging and browning of fresh-cut Cistanche deserticola. The L* value represents the brightness of the fruit. As shown in Figure 1-A, 3 groups 

The L* value of fresh-cut Cistanche deserticola in the cysteine-treated group and the control group showed a downward trend. And throughout the storage period, the L* value of the 1.5 g/L cysteine treatment group was significantly higher than that of the control group (P<0.05), indicating that 1.5 g/L cysteine treatment can effectively alleviate the symptoms of fresh-cut Cistanche deserticola. Reduction in brightness. The a* value indicates the redness and greenness of the fruit. The greater the a* value, the redder the color, and vice versa. As shown in Figure 1-B, during the storage process, the a* value of fresh-cut Cistanche deserticola in each group continued to increase. The a* value of the control group increased rapidly. At the end of storage, the 1.5 g/L cysteine treatment group was 20.1%, 14.3%, and 11.9% lower than the control group, 0.5, and 1.0 g/L cysteine treatment groups, respectively. . As shown in Figure 1-C, during the entire storage process, the b* values of the three cysteine-treated groups and the control group of fresh-cut Cistanche deserticola showed an increasing trend. On the 10th day, 1.5 g/L cysteine The b* value of the amino acid treatment group was 11.8% lower than that of the control group (P<0.05). Description: Treating fresh-cut Cistanche deserticola with 1.5 g/L cysteine can delay the progression of a*, b* value increases, thereby reducing the deepening of the color of fresh-cut Cistanche deserticola.

Fig. 1 Effect of cysteine on L * ,a * ,b * value of fresh-cut Cistanchesherba

2.2 Effect of cysteine treatment on TSS of fresh-cut Cistanche deserticola

TSS can reflect important indicators of fruit maturity and storage stability [21]. As shown in Figure 2, the TSS content in each group showed a downward trend, which may be due to the decrease in soluble solids caused by the metabolism of fresh-cut Cistanche deserticola during storage. After the 2nd day of storage, the TSS content in the 1.5 g/L cysteine treatment group was higher than that in the control group (P<0.05). On the 10th day, the TSS content in the 1.5 g/L cysteine treatment group was 1.41 times that of the control group. . It shows that 1.5 g/L cysteine can effectively maintain the decrease in TSS content of fresh-cut Cistanche deserticola during storage.

2.3 Effect of cysteine treatment on soluble protein of fresh-cut Cistanche deserticola

Soluble protein content can most clearly reflect one of the physiological indicators of cell aging in fruit and vegetable tissues [22]. As shown in Figure 3, the soluble protein content of each group showed an overall downward trend during the entire storage period. The soluble protein content of the three cysteine-treated groups was higher than that of the control group. This may be because cysteine treatment can delay the processing of fresh cuts. The hydrolysis of Cistanche deserticola's soluble protein is reduced, allowing it to maintain better nutritional value. The control group and the 0.5 and 1.0 g/L cysteine treatment groups had peak values on the 2nd day of storage, while the 1.5 g/L cysteine treatment group had a peak value on the 4th day.

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After the second day of storage, the soluble protein content of the 1.5 g/L cysteine treatment group was significantly higher than that of the control group (P<0.05), indicating that the 1.5 g/L cysteine treatment had a greater impact on the soluble protein content. The processing effect is relatively good.

2.4 Effect of cysteine treatment on ASA and GSH contents of fresh-cut Cistanche deserticola

Ascorbic acid is one of the important nutrients in fruits and vegetables. As shown in Figure 4-A, the ASA content in fresh-cut Cistanche deserticola showed a decreasing trend compared to day 0. After day 6, the ASA content in the control group decreased relatively quickly, and the ASA content in the cysteine-treated group was significantly higher than that in the control group (P<0.05). On the 10th day, the ASA content in the 1.5 g/L cysteine treatment group was 2.67 times that of the control group (P<0.05). It follows that cysteine treatment can slow down the decrease in ASA content.

The content of reduced glutathione is closely related to the antioxidant capacity of fruits and vegetables. As shown in Figure 4-B, both the control group and the treatment group showed an upward trend first and then a downward trend. The control group and 0.5 g/L cysteine treatment group had peak values on the 2nd day of storage, and the 1.0 and 1.5 g/L cysteine treatment groups had peak values on the 4th day of storage. On the 10th day, the GSH content of the 1.0 and 1.5 g/L cysteine treatment groups was 47.3% and 47.6% higher than that of the control group (P<0.05). Description: Treatment with 1.0 and 1.5 g/L cysteine can effectively maintain the GSH content of fresh-cut Cistanche deserticola fruits during postharvest storage.

2.5 Effect of cysteine treatment on antioxidant enzyme activity of fresh-cut Cistanche deserticola

As can be seen from Figure 5-A, the POD activity of the three cysteine-treated groups and the control group showed an increasing trend within 0 to 6 days, reaching a peak on the 6th day, with 0.5, 1.0, and 1.5 g/L cysteine treatments. group were 1.39, 2.29, and 2.35 times that of the control group at this time. This may be due to the increase in active oxygen levels in the fruit caused by mechanical damage caused by fresh cutting [23]. The antioxidant mechanism in fresh-cut Cistanche deserticola tissue was triggered. In a state of oxidative stress, POD activity increases. After day 6, the POD activity of the three cysteine-treated groups and the control group began to decrease. On the 2nd to 8th day, the POD activity of the 1.5 g/L cysteine treatment group was higher than that of the control group (P<0.05). On the 10th day of storage, the POD activity of the 1.5 g/L cysteine treatment group was higher than that of the control group. 39.8%. It is further known that cysteine treatment can increase POD activity. This may be due to mechanical damage causing the tissue to produce excessive H2O2, thereby inducing cysteine to increase POD activity and clearing excess H2O2 in a timely manner, which has a positive effect on delaying the aging of fresh-cut Cistanche deserticola. [twenty four].

The accumulation of H2O2 causes oxidative damage to tissues, and CAT can catalyze the decomposition of H2O2 into H2O and O2, thereby reducing the oxidative damage caused by H2O2 [25]. As shown in Figure 5-B, the CAT activity of fresh-cut Cistanche deserticola in the control group showed an overall downward trend during storage. This may be because as the Cistanche deserticola tissue ages during storage, a large amount of reactive oxygen species is produced in the tissue, thereby inhibiting the CAT activity [ 14]. The 3 groups of cysteine treated groups showed a trend of first increasing and then decreasing, with a peak on the 4th day. The 0.5, 1.0, and 1.5 g/L cysteine treated groups were 95.3%, 118.8%, and 194.3% higher than the control group. , after the 4th day, the CAT activity of the three cysteine-treated groups began to decrease. During the entire storage period, the CAT activity of the 1.5 g/L cysteine treatment group was higher than that of the control group. On the 10th day, the CAT activity of the 1.5 g/L cysteine treatment group was 4.13 times that of the control group (P<0.05). . It can be seen that cysteine treatment can induce and increase the CAT activity of fresh-cut Cistanche deserticola and reduce the oxidative damage caused by H2O2.

As shown in Figure 5-C, the APX activity of fresh-cut Cistanche deserticola showed an overall trend of first increasing and then decreasing during storage, with a peak on the 4th day. During the entire storage period, the APX activity of the three cysteine-treated groups was always higher than that of the control group. The APX activity in the 0.5, 1.0, and 1.5 g/L cysteine treatment groups was 1.12, 1.23, and 1.29 times that of the control group. After the 4th day, the APX activity began to decrease. The APX activity in the 1.5 g/L cysteine treatment group was all significant. Higher than the control group (P<0.05). On the 10th day, the APX activity of the 1.5 g/L cysteine treatment group was 2 times that of the control group.

It can be seen that cysteine treatment can induce and increase the APX activity of fresh-cut Cistanche deserticola. GR can reduce oxidized glutathione (GSSG) to GSH, which can scavenge reactive oxygen species, thereby protecting tissues from reactive oxygen species [26]. As shown in Figure 5-D, the GR activity of the control group decreased on the 2nd day of storage and peaked on the 4th day of storage. The three cysteine-treated groups all showed a trend of first increasing and then decreasing. At the end of storage, there was a significant difference between the 1.5 g/L cysteine treatment group and the control group on the 8th and 10th days (P<0.05), which was 4.3 and 4.8 times higher than the control group respectively. After the 4th day of storage, the GR activity of the three cysteine-treated groups was higher than that of the control group, which shows that cysteine can maintain the decrease in GR activity. APX and GR are antioxidant enzymes that use ascorbic acid and oxidized glutathione as substrates respectively to remove excess H2O2 to protect cells from oxidative damage, protect cells from reactive oxygen species, and play an important role in the defense system [27 ].

2.6 Effect of cysteine treatment on PPO enzyme activity of fresh-cut Cistanche deserticola

PPO is one of the main enzymes that causes browning of fresh-cut Cistanche deserticola tissue. As shown in Figure 6, during the entire storage period, the PPO activity of the control group and the treatment group showed a downward trend compared with day 0, and the control group and the 0.5 and 1.0 g/L cysteine treatment groups showed a downward trend on the 2nd and 6th days. Peak value, and there was no significant difference in PPO activity value during storage compared with the control group (P﹥0.05). Perhaps because of the low cysteine concentration, the inhibitory effect on PPO activity is not obvious. The 1.5 g/L cysteine treatment group had peak values on the 4th and 6th days. Except for the 8th day, the PPO activity was lower than that of the control group (P<0.05). At the end of storage, the PPO activity was lower than that of the control group. Low in control group

61.9%. It shows that the cysteine solution concentration of 1.5 g/L has a significant inhibitory effect on the PPO activity of fresh-cut Cistanche deserticola, and also has a positive effect on delaying the browning of fresh-cut Cistanche deserticola.

2.7 Effect of cysteine treatment on total phenolic content and PAL activity of fresh-cut Cistanche deserticola

Phenolic substances are widely distributed in fruits and vegetables. They are not only important antioxidant secondary metabolites of fruits and vegetables themselves, but also beneficial to human health [28]. It can be seen from Figure 7-A that the total phenolic content of the 3 cysteine-treated groups and the control group decreased on the second day of storage, and then peaked on the 6th day in the control group, while the 3 cysteine-treated groups peaked on the 6th day. The peak value appeared on day 4, and the total phenolic content was higher than that of the control group. It may be because cysteine treatment can induce the synthesis and accumulation of phenolic substances in fresh-cut Cistanche deserticola. On the 10th day of storage, the total phenolic content of the 1.5 g/L cysteine treatment group was significantly higher than that of the control group (P<0.05), which was 1.96 times that of the control group. It can be seen that cysteine treatment can also delay the development of fresh-cut Cistanche deserticola The total phenolic content of Chengdu decreased.

PAL is involved in the biosynthesis of a variety of secondary metabolites, such as phenolics, and is one of the key enzymes regulating the phenylpropanoid pathway in fruits and vegetables [29]. After fruits and vegetables are freshly cut, mechanical damage will activate phenylpropanoid metabolism, induce the synthesis of phenolic substances, and indirectly cause browning [30]. As shown in Figure 7-B, the PAL activity of the three cysteine-treated groups and the control group showed an overall upward trend. After the 4th day of storage, the increase rate of PAL activity in the 1.5 g/L cysteine-treated group accelerated, and the control group showed an overall upward trend. The PAL activity of each group was lower than that of the cysteine-treated group, possibly because cysteine treatment can induce an increase in PAL activity and increase the synthesis and accumulation of phenolic substances.

2.8 Effect of cysteine treatment on H2O2 and MDA contents of fresh-cut Cistanche deserticola

As shown in Figure 8-A, during storage, the H2O2 content of fresh-cut Cistanche deserticola showed an overall trend of first increasing and then decreasing. The H2O2 content of the control group was always higher than that of the 3 cysteine-treated groups. Before the 8th day, the H2O2 content in the 1.5 g/L cysteine treatment group was significantly lower than that in the control group (P<0.05). On the 10th day, the H2O2 content in the 1.5 g/L cysteine treatment group was 29.7 lower than the control group. % (P＜0.05). During the entire storage period, the H2O2 content in the cysteine-treated group was lower than that in the control group. It can be seen that cysteine treatment can reduce the accumulation of hydrogen peroxide during the storage of fresh-cut Cistanche deserticola.

MDA content can be used to reflect the degree of cell membrane lipid peroxidation and can also indirectly measure the degree of cell damage [31]. It can be seen from Figure 8-B that the MDA content of the three cysteine-treated groups and the control group showed a significant upward trend, indicating that as the storage time increases, the cell membrane lipid peroxidation of fresh-cut Cistanche deserticola increases. On the second day of storage, the MDA content results of the 0.5 and 1.0 g/L cysteine treatment groups and the control group were not significant (P>0.05), while the MDA content of the 1.5 g/L cysteine treatment group was significantly lower. in the control group. On the 10th day of storage, the 0.5, 1.0, and 1.5 g/L cysteine treatment groups were 29.2%, 48.7%, and 63.9% lower than the control group, respectively. Throughout the storage period, the cysteine-treated group

The MDA content was lower than that of the control group. Cysteine treatment can effectively slow down the accumulation of MDA in fresh-cut Cistanche deserticola, reduce the degree of lipid peroxidation of its cell membrane, better maintain the integrity of the cell membrane, and delay the aging and deterioration of fresh-cut Cistanche deserticola.

Fig. 8 Effect of cysteine on H2 O2 and MDA content of fresh-cut Cistanchesherba

3 Discussion

Color, soluble protein, soluble solids, and ascorbic acid are important indicators that affect the storage quality of fruits and vegetables [32]. Research has found that cysteine treatment of fresh-cut Cistanche deserticola can delay the decrease in L* value (brightness) and the increase in a* (redness) and b* (yellowness) values, and the concentration of 1.5 g/L cysteine The processing effect is relatively the best. 1.5 g/L cysteine can also effectively alleviate the decrease in soluble protein, soluble solids, and ascorbic acid content of fresh-cut Cistanche deserticola during storage, and has a positive impact on maintaining the storage quality of fresh-cut Cistanche deserticola.

The metabolism of active oxygen in fruits and vegetables is closely related to the storage quality and length of fruits and vegetables [33]. Due to mechanical damage to fresh-cut Cistanche deserticola, the tissue structure is destroyed, which will produce a series of adverse physiological and biochemical reactions, such as the accumulation of reactive oxygen species, which directly affects the storage quality [34]. There are two types of ROS scavenging systems in fruit and vegetable cells: one is reactive oxygen species scavenging enzymes, including POD, CAT, APX, GR, etc.; the other is non-enzymatic scavenging systems, including antioxidant substances such as ASA and GSH [35]. This study found that 1.5 g/L cysteine treatment can effectively enhance the activities of POD, CAT, APX, and GR during the storage of fresh-cut Cistanche deserticola, thereby reducing the accumulation of reactive oxygen species and mitigating oxidative damage of fresh-cut Cistanche deserticola.

The research results of Chen Chen [14] also showed that cysteine treatment can induce and increase the activities of antioxidant enzymes such as POD, CAT, APX, and GR during the storage of fresh-cut apples, and delay the aging and browning of fresh-cut apples. The research results of Feng Chengcheng [15] showed that cysteine treatment of fresh-cut purple sweet potatoes can inhibit POD enzyme activity. The difference in results may be related to the types of fruits and vegetables and different processing conditions. In addition, endogenous antioxidant substances ASA and GSH will eliminate the production of ROS in tissues under normal physiological conditions and ensure fruit quality [36]. In this study, 1.5 g/L cysteine treatment can effectively delay the decline of ASA and GSH content, maintain high antioxidant content, enhance the fruit's reactive oxygen scavenging ability, thereby reducing oxidative damage.

PPO can catalyze the combination of oxygen and polyphenols in fruits and vegetables to form quinones. The quinones polymerize to form brown sediments, causing browning of fruits and vegetables [19]. Treatment of fresh-cut Cistanche deserticola with 1.5 g/L cysteine can effectively inhibit PPO enzyme activity, thereby delaying the occurrence of browning. Lu Fan [18] and Wei Jie [11] found that controlled atmosphere storage can inhibit the PPO activity of fresh-cut Cistanche deserticola, slow down browning, and better maintain the storage quality of fresh-cut Cistanche deserticola. Mechanical damage can induce an increase in PAL activity in fresh-cut fruits and vegetables and increase the synthesis of phenolic substances [37]. This study found that the PAL enzyme activity and total phenolic content of fresh-cut Cistanche deserticola after cysteine treatment were higher than those of the control group, and the 1.5 g/L cysteine treatment concentration was relatively optimal, indicating that cysteine can increase the production of fresh-cut Cistanche deserticola. Mechanical damage induces the effect of increasing the PAL activity of Cistanche deserticola and accumulating total phenolic content.

4 Conclusion

This study shows that 1.5 g/L cysteine treatment can effectively increase the activities of POD, CAT, APX, and GR during the storage of fresh-cut Cistanche deserticola, delay the decrease in the contents of soluble protein, TSS, ASA, and GSH, and inhibit the interaction between MDA and H2O2. accumulation, better maintaining the storage quality of fresh-cut Cistanche deserticola.

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