Nanocomposite packaging delays lignification of Flammulina velutipes by regulating phenylpropanoid pathway and mitochondrial reactive oxygen species metabolisms

https://doi.org/10.1016/j.postharvbio.2020.111360Get rights and content

Highlights

  • Nanocomposite packaging was used for F. velutipes storage.

  • Nanocomposite packaging inhibited enzymes activities of phenylpropanoid pathway.

  • The accumulation of mitochondrial ROS and Ca2+ was inhibited.

  • Nanocomposite packaging effectively inhibited lignification of F. velutipes.

Abstract

Lignification is an important inducement of quality deterioration of postharvest Flammulina velutipes. In this study, phenylpropanoid pathway and mitochondrial reactive oxygen species (ROS) metabolisms were taken as breakthrough points to investigate the lignification mechanism in harvested F. velutipes packaged in nanocomposite packaging material (Nano-PM). In comparison with polyethylene packaging material (Normal-PM) and no packaging material (No-PM), Nano-PM prevented the decrease of L* value and the increase of firmness. Nano-PM also maintained a better microstructure. Furthermore, Nano-PM reduced the deposition of lignin by suppressing the enzymes activities involved in phenylpropanoid pathway. In addition, the regulation of ROS in mitochondria alleviated the accumulation of Ca2+ and inhibited the programmed cell death (PCD) process, which ultimately delayed the lignification process. These results indicated that Nano-PM delayed the lignification process by regulating phenylpropanoid pathway and the accumulation of ROS in mitochondria.

Introduction

Flammulina velutipes is popular among consumers due to its delicious taste and rich nutrition. Currently, with the advancement in industrial cultivation technology, F. velutipes has become one of the five worldwide cultivated edible mushrooms. Nevertheless, fresh F. velutipes is prone to rapid post growth in the process of storage due to transpiration and respiration, which leads to cap opening, stipe elongation and lignification (Fang et al., 2016b). Thus, various preservation methods are applied to extend the shelf life of F. velutipes. Nanocomposite packaging (Nano-PM) is one of the convenient and economical methods for shelf life extension of F. velutipes. Nano-PM effectively inhibits the respiration of F. velutipes by regulating the atmosphere inside the packaging (O2: 2.5–3.9 %, CO2: 7.0–8.4 %) (Fang et al., 2016a). Besides, it had been proven that Nano-PM could postpone senescence of F. velutipes by regulating protein expression, energy metabolism, extracellular ATP and PCD in our previous studies (Fang et al., 2017; Shi et al., 2020; Yang et al., 2019). Nonetheless, the mechanism of lignification regulation by Nano-PM is unclear.

Research has shown that lignification is a process of lignin accumulation that could impact negatively on texture, maturity, browning, taste and nutritional value of postharvest fruit and vegetables (Jiang et al., 2010; Schäfer et al., 2016; Toivonen and Brummell, 2008; Wang et al., 2017). Phenylpropanoid pathway is mainly responsible for metabolism of secondary metabolites in plants including lignin, thus, it has an important bearing on lignification process (Chezem et al., 2017; Gou et al., 2019). Besides, research has demonstrated that lignification could be effectively delayed by inhibiting enzymes activities involved in the phenylpropanoid pathway (Luo et al., 2007; Toscano et al., 2018). In our previous studies, we found that lignin content increased in F. velutipes during storage period. However, the phenylpropanoid pathway regulated by Nano-PM is unclear.

Excessive accumulation of ROS induce senescence in fruit and vegetables (Vicente et al., 2006). In addition, there is a positive correlation between lignin deposition and ROS level, indicating that ROS may regulate the synthesis of lignin (Denness et al., 2011). Moreover, ROS could accelerate the lignification process by increasing the enzymes activities related to phenylpropanoid pathway and activating the PCD process of postharvest bamboo shoots (Li et al., 2019). Nonetheless, the relationship between lignification and mitochondrial ROS metabolism in postharvest F. velutipes is still unclear.

Therefore, color, firmness, microstructure and lignin content as well as enzymes, linked with phenylpropanoid pathway, were determined to assess the impact of Nano-PM on lignification of postharvest F. velutipes. Besides, the accumulation of ROS and Ca2+ in the mitochondria and PCD were also determined to further elucidate the effect of Nano-PM on lignification.

Section snippets

Preparation of mushroom

Flammulina velutipes free from damage was transported to the laboratory within one hour upon harvesting from Jiangsu Tianfeng Biological Technology Co., Ltd, China. Nano-PM comprising of 0.30 % nano Ag, 0.35 % nano TiO2, 0.25 % nanoattapulgite and 0.10 % nano SiO2 and Normal-PM containing polyethylene bags were made on the basis of our previous study (Fang et al., 2016b). The bags measured 25 × 25 cm2 with a 40 μm thickness. F. velutipes of uniform size (stipe length: 15 ± 1 cm, cap diameter:

Sensory quality and microstructure observation

Color and firmness are iconic features to evaluate the edible quality of F. velutipes, which are closely linked to lignification. As shown in Fig. 1A, L* continuously decreased during storage period in all the groups. At 15 d, L* in Nano-PM, Normal-PM and No-PM decreased from 84.15 to 76.06, 73.17 and 65.55 respectively (P < 0.05). Thus, Nano-PM effectively delayed browning compared with the other two control groups. On the other hand, firmness continuously increased during the storage time.

Conclusion

In this study, Nano-PM delayed lignin deposition by inhibiting enzyme activities associated with phenylpropanoid pathway, thus effectively maintained sensory quality and microstructure of F. velutipes. Besides, Nano-PM effectively maintained higher H2S content by regulating LCD and DCD activities, which was closely linked with lignification and ROS metabolism. Additionally, Nano-PM effectively maintained Ca2+ homeostasis and delayed PCD process by inhibiting the accumulation of mitochondrial

CRediT authorship contribution statement

Changzhou Zuo: Conceptualization, Methodology, Investigation, Data curation, Writing - original draft, Writing - review & editing. Qiuhui Hu: Methodology, Investigation. Anxiang Su: Investigation, Validation. Hui Xu: Investigation, Validation. Xiuting Li: Investigation, Validation. Alfred Mugambi Mariga: Writing - review & editing. Wenjian Yang: Conceptualization, Supervision, Writing - original draft, Writing - review & editing, Project administration.

Declaration of Competing Interest

There are no conflicts of interests to declare.

Acknowledgments

This work was financially supported by the Natural Science Foundation of Jiangsu Province for Excellent Youth Scholars (No. BK20180092), National Natural Science Foundation of China (No. 31871853), Natural Science Research Program for Higher Education Universities in Jiangsu Province (NO. 18KJA550002), Postgraduate Research & Practice Innovation Program of Jiangsu Province (KYCX19_1404) and the Priority Academic Program Development of Jiangsu Higher Education Institutions (PAPD).

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