Artigo Sobre Processamento Das Frutas: Maça

This work reviews the main factors contributing to the occurrence of postharvest fruit peel browning, including

water loss, chilling injury, disease and mechanical damage. In addition, the present work discusses the potential

biochemical mechanisms involved in the occurrence of postharvest peel browning, mainly including insufficient

energy supply and reactive oxygen species (ROS) burst. This work updates the progress of methods to control the

occurrence of postharvest fruit peel browning, which provides an important reference role to reduce postharvest

fruit losses. Notably, although the direct causative factor of peel browning in different fruit is PPO-mediated

enzymatic browning of phenolics, the specific substrates of PPO are different in various fruit peels. Some conventional postharvest preservation methods have also shown promising effect in inhibiting postharvest fruit peel

browning, while the next batch of candidates for inhibiting peel browning of postharvest fruit are some small

molecule substances that have antioxidant activity and improve cell energy supply. However, to better inhibit the

occurrence of peel browning, some combinations of conventional postharvest preservation methods should be

considered in future studies, which might achieve better and more effective results.

1. Introduction

Fresh fruit with their attractive flavor and excellent nutritional value

are indispensable foods in people’s daily life (Li et al., 2021; Zhang et al.,

2021a). However, there is a significant loss of fresh fruit in postharvest

logistics, which is mainly due to reduced commodity value associated

with their rapid senescence and decay (Zhang et al., 2021b). Obvious

quality deterioration occurring in the postharvest stage of fresh fruit

involve the loss of sensory and nutritive attributes. Browning, as one of

the most perceivable features of quality deterioration in many intact and

fresh-cut fruits, has restricted the development of fruit postharvest industry (Zhang et al., 2015; He et al., 2020, 2021c). It is well known that

browning of food is divided into enzymatic browning and

non-enzymatic browning, the latter mainly involves the browning reactions that occur when foods are heated, such as the Maillard reaction

and caramelization (Manzocco et al., 2020). Fresh fruit mainly involve

in enzymatic browning during storage (Ma et al., 2017). Take fresh-cut

fruit for example, they undergo minimal processing (peeling, dicing,

slicing, etc.) and suffer large-scale mechanical injury, cell contents

leakage and exposure to oxygen, resulting in the polyphenol oxidase

(PPO)-catalyzed oxidation of phenolics and formation of brown

pigment-like substances and melanin (Singh et al., 2018). How to

effectively inhibit PPO activity has been a focus of solving browning

issue of fresh-cut products (Wang et al., 2021a; Ma et al., 2021).

Although much attention has been paid to browning of fresh-cut

fruit, intact fruit still dominates the market of fresh fruit that can

often occur internal browning and peel browning during storage and

marketing (Xu et al., 2020; He et al., 2020). Fruit peel quality is a direct

indicator of the freshness of the fruit, but also the primary factor

affecting the consumer’s purchase. Bright peel color indicates ideal fruit

freshness (He et al., 2020). Compared with internal browning, peel

browning of fresh fruit may be easily detected by consumers, thus

reducing its commercial attribute. The peel of mature fruit is generally

composed of three layers including inner, middle and outer. Different

fruit peel structure is various. For example, longan and lychee possess

inedible hard peel, while the peel of apple belongs to edible tissue (Ali

et al., 2016; Li et al., 2021). In addition to mechanical injury, the

senescence process, low temperature, low oxygen and water loss can

also cause browning of the fruit peel (Fig. 1) (Ali et al., 2019a; He et al.,

2020).

Several strategies are currently being developed by scientists to

counteract the occurrence of fruit peel browning. Among them, some

4. Methods to control postharvest fruit browning

Commonly, postharvest fruit browning due to senescence or chilling

injury is the main factor leading to the loss of commercial value of

postharvest fruit. Therefore, more research in the field of postharvest

fruit preservation has been conducted through some physical or chemical treatments to regulate postharvest fruit physiological metabolism,

extend the shelf life of postharvest fruit, and inhibit the occurrence of

peel browning.

4.1. Physical treatments

4.1.1. Temperature conditioning (TC)

Postharvest fruit temperature conditioning refers to some of the lowtemperature sensitive fruit in low-temperature storage through a period