Avocado Fruit Quality Management during the Postharvest Supply Chain

Shelf-Life Management and Ripening Assessment of 'Hass' Avocado (Persea americana) Using Deep Learning Approaches

Avocado production is mostly confined to tropical and subtropical regions, leading to lengthy distribution channels that, coupled with their unpredictable post-harvest behavior, render avocados susceptible to significant loss and waste. To enhance the monitoring of 'Hass' avocado ripening, a data-driven tool was developed using a deep learning approach. This study involved monitoring 478 avocados stored in three distinct storage environments, using a 5-stage Ripening Index to classify each fruit's ripening phase based on their shared characteristics. These categories were paired with daily photographic records of the avocados, resulting in a database of labeled images. Two convolutional neural network models, AlexNet and ResNet-18, were trained using transfer learning techniques to identify distinct ripening indicators, enabling the prediction of ripening stages and shelf-life estimations for new unseen data. The approach achieved a final prediction accuracy of 88.8% for the ripening assessment, with 96.7% of predictions deviating by no more than half a stage from their actual classifications when considering the best side of the samples. The average shelf-life estimates based on the attributed classifications were within 0.92 days of the actual shelf-life, whereas the predictions made by the models had an average deviation of 0.96 days from the actual shelf-life.

Field and postharvest application of microencapsulated Yamadazyma mexicana LPa14: anthracnose control and effect on postharvest quality in avocado (Persea americana Mill. cv. Hass)

BACKGROUND

Anthracnose caused by species of Colletotrichum is the most important disease of avocado fruit. The quiescent infection develops in the field, hence, its control from the preharvest stage is necessary. The field application of microencapsulated Yamadazyma mexicana LPa14 could prevent the establishment of Colletotrichum gloeosporioides and reduce the losses in avocado production. This study aimed to evaluate the effectiveness of microencapsulated Y. mexicana applied in the field and postharvest for the anthracnose control in avocado, to evaluate the population dynamics of Y. mexicana in flowers and fruits and the effect of the yeast on the avocado quality.

RESULTS

The concentrations of microencapsulated Y. mexicana after field application ranged from 4.58 to 6.35 log CFU g-1 . The population of microencapsulated yeast in flowers and fruits was always higher than treatments with fresh cells. Preharvest application of fresh and microencapsulated Y. mexicana significantly reduced the severity of anthracnose by 71-80% and 84-96%, respectively, in avocado fruits stored at 25 °C. Moreover, at 6 °C and ripening at 25 °C, the fresh yeast reduced the severity by 87-90% and the microencapsulated yeast by 91-93%. However, yeast treatments applied in the field + postharvest under cool conditions were more effective in reducing 100% of anthracnose. Treatments did not negatively affect the quality parameters of the avocado fruits.

CONCLUSION

Yamadazyma mexicana microencapsulated by electrospraying is a promising bioformulation for the management of anthracnose in avocados at preharvest and postharvest levels. Yamadazyma mexicana offers a new biological control solution for growers in avocado orchards. © 2024 Society of Chemical Industry.

Arabic gum/chitosan/Zn-NPs composite film maintains the quality of Hass avocado fruit by delaying ripening and activating enzymatic defense mechanisms

Avocado fruit is a climacteric fruit that has a short life after harvest. Chitosan (Ch) and Arabic gum (AG) have a pronounced effect on the storability of fruits. This investigation aimed to determine the effect of individual or combined use of Ch and AG as well as Ch/AG enriched with 2, 4, 8% Zn-NPs on physio-biochemical attributes and antioxidant capacity of Hass avocado fruit during cold storage (7 °C). The result showed that Ch or AG alone succeeded in maintaining fruit quality of Hass fruit during cold storage. Also, combined application of Ch/AG was more effective than individual application of Ch or AG in reducing fruit weight and polyphenol oxidase activity (PPO) as well as increasing total antioxidant capacity (TAC) and malondialdehyde (MDA). Moreover, Ch/AG coating enriched with 8% Zn-NPs recorded the lowest fruit weight loss, fruit decay %, TSS fruit content, fruit firmness and improved fruit skin and pulp color significantly compared to Ch/AG and control. Coating with Ch/AG/2%Zn NPs recorded the highest peroxidase (POD) activity, while Ch/AG/8% Zn-NPs recorded the highest TAC and the lowest PPO activity. Moreover, enriched Ch/GA with Zn-NPs recorded the highest CAT and POD activity compared to the control. This study shows the efficiency of Ch/AG enriched with Zn-NPs on preserving Hass avocado fruit quality during cold storage by delaying ripening process and activating enzymatic defense mechanisms.

A Functional End-Use of Avocado (cv. Hass) Waste through Traditional Semolina Sourdough Bread Production

In recent years, a main goal of research has been to exploit waste from agribusiness industries as new sources of bioactive components, with a view to establishing a circular economy. Non-compliant avocado fruits, as well as avocado seeds and peels, are examples of promising raw materials due to their high nutritional yield and antioxidant profiles. This study aimed to recycle avocado food waste and by-products through dehydration to produce functional bread. For this purpose, dehydrated avocado was reduced to powder form, and bread was prepared with different percentages of the powder (5% and 10%) and compared with a control bread prepared with only semolina. The avocado pulp and by-products did not alter organoleptically after dehydration, and the milling did not affect the products' color and retained the avocado aroma. The firmness of the breads enriched with avocado powder increased due to the additional fat from the avocado, and alveolation decreased. The total phenolic content of the fortified breads was in the range of 2.408-2.656 mg GAE/g, and the antiradical activity was in the range of 35.75-38.235 mmol TEAC/100 g (p < 0.0001), depending on the percentage of fortification.

Quantification of Dry Matter Content in Hass Avocado by Near-Infrared Spectroscopy (NIRS) Scanning Different Fruit Zones

Accurate dry matter determination (DM) in Hass avocados is vital for optimal harvesting and ensuring fruit quality. Predictive models based on NIRS need to capture fruit DM gradient. This work aimed to determine the DM content in Hass avocado whole by NIRS scanning different fruit zones. Spectra were recorded for each zone of the fruit: peduncle (P), equator (E), and base (B). The calibration and validation included fruit from different orchards in two harvest cycles. The results show a DM gradient within the fruit: 24.47% (E), 24.68% (B), and 24.79% (P). The DM gradient was observed within the spectra using the RMSi (root mean square) criterion and PCA. The results show that at least one spectrum per fruit zone was needed to represent the variability within the fruit. The performances of the calibration using the whole set of data were R2: 0.74 and standard error of cross-validation (SECV) = 1.18%. In the validation stage using independent validation sets, the models showed similar performance (R2: 0.75, SECV 1.15%) with low values of the standard error of prediction (SEP): 1.62%. These results demonstrate the potential of near-infrared spectroscopy for high-throughput sorting of avocados based on their commercial quality.

Putrescine with Aloe vera gel coating improves bioactive compounds and quality of table grape under cold storage

Abstract

Bioactive compounds and quality were determined in table grape (Vitis vinifera cv. 'Yaghouti') at storage period after treatment with 2.0 and 3.0 mM putrescine (PUT) and 1:25 and 1:33 Aloe vera gel (AVG). The PUT treatments were given by foliar application on the tree and followed by AVG immersion then storage up to 36 days at 4 ± 0.5 °C. Both treatments retained significantly higher firmness, ascorbic acid, anthocyanin, antioxidant, phenolic content, and sensory attributes as compared with control berries under the storage conditions. Combined application of PUT + AVG showed a better response in retaining vitamin C, total antioxidants, phenolic contents, organoleptic evaluation, enzymes, and fruit firmness than only treated berries with PUT or AVG or untreated berries. The impacts of PUT2.0 mM + AVG 25% treatments were found more pronounced after 36 days of storage in bioactive compounds and sensory attributes.

Graphical abstract

Characterization and application of a coating of starch extracted from avocado (Persea americana L. cv. Hass) seeds as an alternative to reduce acrylamide content in French fries

The starch extracted from avocado (Persea americana L. cv. Hass) seeds was characterized and used in the preparation of an edible coating to reduce the oil uptake and acrylamide content in French fries. Starch characterization was carried out using Differential Scanning Calorimetry, Fourier transform infrared spectrophotometry, gelatinization, and scanning electron microscopy. Uncoated (UFF) and coated (CFF) French fries were compared and evaluated for moisture, water activity (Aw), fat, color, firmness, acrylamide content, and sensorial analysis. The extracted starch presented a high crystalline structure and good stability to mechanical work and heat treatments. The CFF French fries showed significantly higher Aw, color parameter a*, but lower luminosity and acrylamide content than UFF samples. Similarly, the CFF samples tended to decrease the fat content, although without statistical differences. Avocado seed starch can be an economical and technically feasible alternative to the food industry as an effective coating to reduce acrylamide content in French fries.

First Look Into the Ambrosia Beetle-Fungus Symbiosis Present in Commercial Avocado Orchards in Michoacán, Mexico

Most beetle-fungus symbioses do not represent a threat to agricultural and natural ecosystems; however, a few beetles are able to inoculate healthy hosts with disease-causing fungal symbionts. Here, we report the putative nutritional symbionts associated with five native species of ambrosia beetles colonizing commercial avocado trees in four locations in Michoacán. Knowing which beetles are present in the commercial orchards and the surrounding areas, as well as their fungal associates, is imperative for developing a realistic risk assessment and an effective monitoring system that allows for timely management actions. Phylogenetic analysis revealed five potentially new, previously undescribed species of Raffaelea, and three known species (R. arxi, R. brunnea, R. fusca). The genus Raffaelea was recovered from all the beetle species and across the different locations. Raffaelea lauricola (RL), which causes a deadly vascular fungal disease known as laurel wilt (LW) in Lauraceae species, including avocado, was not recovered. This study points to the imminent danger of native ambrosia beetles spreading RL if the pathogen is introduced to Mexico's avocado orchards or natural areas given that these beetles are associated with Raffaelea species and that lateral transfer of RL among ambrosia beetles in Florida suggests that the likelihood of this phenomenon increases when partners are phylogenetically close. Therefore, this study provides important information about the potential vectors of RL in Mexico and other avocado producing regions. Confirming beetle-fungal identities in these areas is especially important given the serious threat laurel wilt disease represents to the avocado industry in Mexico.

Purification and characterization of avocado (Persea americana) polyphenol oxidase by affinity chromatography

Polyphenol oxidase (PPO) enzyme was purified from avocado (Persea americana) by ammonium sulfate precipitation 0-80%, dialysis and affinity chromatography. Characterization studies were performed with catechol (0.10 M, pH: 7.2, 37 °C), 4-methyl catechol (0.10 M, pH: 6.0, 37 °C), pyrogallol (0.02 M, pH: 8.5, 5 °C), chlorogenic acid (0.20 M, pH: 6.8, 10 °C) and caffeic acid (0.20 M, pH: 8.5, 10 °C), respectively. V_max and K_M values were determined for catechol (15789.96 U*mL^-1*min^-1, 10 mM), 4-methyl catechol (6768.40 U*mL^-1*min^-1, 2 mM), pyrogallol (6802.72 U*mL^-1*min^-1, 4 mM), chlorogenic acid (1377.97 U*mL^-1*min^-1, 14.29 mM) and caffeic acid (2567.24 U*mL^-1*min^-1, 5 mM). PPO was purified as 147.73-fold and 154.00-fold by Sepharose 4B-L-Tyrosine-p-aminobenzoic acid and Sepharose-6B-L-Tyrosine-p-aminobenzoic acid, respectively. 4B isolated PPO gave two bands at 35 and 50 kDa in SDS-PAGE while visible and slightly visible bands at 50-70 kDa and 100 kDa in Native-PAGE. 6B isolated PPO gave bands as distinctively at 50 kDa and unclearly at around 35 kDa in SDS-PAGE while visible and slightly visible bands at 50-70 and 100 kDa in Native-PAGE. The synthesis of original 6B-affinity gel and no any study found in literature on affinity purification of avocado PPO show importance of our study.

A Systematic Review of Sustainable Fresh Fruit and Vegetable Supply Chains

Fresh fruit and vegetables are crucial for human health. Their fibrous structure and high nutritional value are essential for people’s well-being. This study aims to provide a review of the current state of knowledge and practices regarding fresh fruit and vegetable supply chains (FFVSC). The reviewed papers are divided into categories according to their findings, research purposes, tools and messages used. Our objective is to guide both academics and practitioners by pointing out significant streams of research with respect to these categories. For a better understanding, these subgroups are essentially based on their common research purpose, and the tools and methods they adopted are explained. Therefore, this study sheds light on research related to FFVSCs for those who are new to this area or planning to conduct in-depth research on directions suggested by studies in this area. The related literature was classified into eight categories: namely, (1) value chain indicators of FFVSCs, (2) food-related problems/postharvest losses along FFVSCs, (3) roles of parties involved in the FFV value chain, (4) review papers, (5) technological trends in FFVSCs, (6) packaging issues of FFVSCs, (7) logistics solutions of FFVSCs, and (8) sustainable FFVSCs. Details on the tools and methods employed in these studies are summarized in Appendix B. To the best of the authors’ knowledge, the related literature lacks a comprehensive review that investigates different aspects of FFVVCs in detail. Thus, this study contributes towards a better understanding of the related literature and can be used as a guide for future studies.

Non-Chemical Treatments for the Pre- and Post-Harvest Elicitation of Defense Mechanisms in the Fungi-Avocado Pathosystem

The greatest challenge for the avocado (Persea americana Miller) industry is to maintain the quality of the fruit to meet consumer requirements. Anthracnose is considered the most important disease in this industry, and it is caused by different species of the genus Colletotrichum, although other pathogens can be equally important. The defense mechanisms that fruit naturally uses can be triggered in response to the attack of pathogenic microorganisms and also by the application of exogenous elicitors in the form of GRAS compounds. The elicitors are recognized by receptors called PRRs, which are proteins located on the avocado fruit cell surface that have high affinity and specificity for PAMPs, MAMPs, and DAMPs. The activation of defense-signaling pathways depends on ethylene, salicylic, and jasmonic acids, and it occurs hours or days after PTI activation. These defense mechanisms aim to drive the pathogen to death. The application of essential oils, antagonists, volatile compounds, chitosan and silicon has been documented in vitro and on avocado fruit, showing some of them to have elicitor and fungicidal effects that are reflected in the postharvest quality of the fruit and a lower incidence of diseases. The main focus of these studies has been on anthracnose diseases. This review presents the most relevant advances in the use of natural compounds with antifungal and elicitor effects in plant tissues.

Quality Evaluation of the Ready-to-Eat Avocado cv. Hass

Consumer interest in avocado fruit has increased in the last decade in Europe. Nutritional and quality attributes affect the choice of these fruits, whose characteristics must also be maintained in the postharvest period. The preference regarding the feasibility of eating ripe fruits can assure and improve the success of the emerging marketing of avocados. The exposure of fruits to exogenous ethylene (C2H4) treatment can accelerate the process of fruit ripening. The aim of this work was at improving the existing knowledge about the quality traits of avocado cv. Hass fruits at the ready-to-eat stage. The most important qualitative traits (weight loss, dry matter content, hardness pulp, and external and internal fruit colour) were evaluated up to 96 hours, maintaining the fruit at two different temperatures, T1 (+8°C) and T2 (+17°C). A trained sensory panel was conducted at 96 hours to confirm the quality of avocado cv. Hass ripened with exogenous C2H4.

‘Hass’ Avocado Internal Disorders under Simulated Export Conditions and Its Relationship with Flesh Mineral Content and Preharvest Variables

The most important issues that affect consumer fruit acceptance in the ‘Hass’ avocado international market are flesh disorders. These defects can be influenced by both pre- and postharvest factors. The aim of this work was to evaluate the effect of the harvest season, storage time, mineral content, and preharvest variables on internal fruit disorders. Here, fruit was sampled from four farms in Antioquia (Colombia) at 22%, 26%, and 30% dry matter (DM) content. Samples were stored and ripened under simulated export conditions. Then, flesh bruising, flesh discoloration, body rots, vascular browning, stem end rot, and mineral content were assessed. The results showed that flesh disorders differ among farms and by harvest index and storage time. The most frequent defects found were vascular browning and stem end rot. Boron, calcium, nitrogen, manganese, magnesium, and potassium have a strong relationship with flesh disorders. Therefore, high boron and calcium contents, as well as a harvest at 26% DM, can substantially reduce avocado flesh disorders and improve internal fruit quality. Farmers that had a high flesh and soil mineral content and low rainfall and temperature produced fruits with fewer internal disorders.

Insights into Drivers of Liking for Avocado Pulp (Persea americana): Integration of Descriptive Variables and Predictive Modeling

Trends in new food products focus on low-carbohydrate ingredients rich in healthy fats, proteins, and micronutrients; thus, avocado has gained worldwide attention. This study aimed to use predictive modeling to identify the potential sensory drivers of liking for avocado pulp by evaluating acceptability scores and sensory descriptive profiles of two commercial and five non-commercial cultivars. Macronutrient composition, instrumental texture, and color were also characterized. Trained panelists performed a descriptive profile of nineteen sensory attributes. Affective data from frequent avocado adult consumers (n = 116) were collected for predictive modeling of an external preference map (R² = 0.98), which provided insight into sensory descriptors that drove preference for particular avocado pulps. The descriptive map explained 67.6% of the variance in sensory profiles. Most accepted pulps were from Hass and Colin V-33; the latter had sweet and green flavor notes. Descriptive flavor attributes related to liking were global impact, oily, and creamy. Sensory drivers of texture liking included creamy/oily, lipid residue, firmness, and cohesiveness. Instrumental stickiness was disliked and inversely correlated to dry-matter and lipids (r = -0.87 and -0.79, respectively). Color differences (∆E_ab*) also contributed to dislike. Sensory-guided selection of avocado fruits and ingredients can develop products with high acceptability in breeding and industrialization strategies.

Recent advances in the use of edible coatings for preservation of avocados: A review

Avocados (Persea americana) are a fruit, whose shelf-life is jeopardized by rapid ripening and fungal diseases, which heighten the necessity for postharvest treatments. The use of refrigeration during storage and transport helps delay the ripening process and phytopathogen growth but it is not enough to attenuate the problem, especially once avocados are placed in ambient temperatures. Fungicides are effective in controlling fungal prevalence, but their possible adverse environmental and human health effects have spurred interest in finding safer, natural substitutes. The objective of this paper is to review recent advances and trends in the use of edible coatings as a safe alternative to preserve and extend avocados shelf-life. Edible biopolymer coatings have gained considerable attention due to their ability to extend fruit and vegetable shelf-life. These coatings are a novel type of biodegradable primary packaging made from biological compounds like polysaccharides, proteins, lipids, and other polymers. Coatings are considered nonactive if they only form a physical barrier, separating avocados from their immediate environment, controlling gas and moisture transfer. Active coatings can contain supplementary ingredients with additional properties like antioxidant and antifungal activity. The application of edible coatings shows promising potential in extending avocado shelf-life, replacing synthetic fungicides and reducing economic losses from avocado spoilage.

Postharvest supply chain losses: a state-of-the-art literature review and bibliometric analysis

Purpose

The literature review of post-harvest supply chain (PHSC) losses is carried out and analyzed in this paper followed by bibliometric analysis of the literature.

Design/methodology/approach

The literature survey is performed across various dimensions such as PHSC losses, PHSC risks and PHSC sustainability (waste management and waste reduction). One hundred thirty research articles during the period of 1989–2020 were considered for the review.

Findings

The PHSC losses have been identified in this literature survey. The calculation and mitigation strategies stated by various researchers in the literature are addressed. The important loss mitigation dynamics are also presented to reduce the PHSC losses and to improve food availability.

Research limitations/implications

The major focus is given on the PHSC of agriculture produces. However, research articles from fish and meat supply chain are excluded as they follow a different perishability curve.

Practical implications

The current work will add value to the agriculture supply chain literature, provide a platform for PHSC losses and provide assistance/guideline toward loss calculation, loss mitigation, improved rural employability, improved rural entrepreneurship and improved revenue generation.

Social implications

The performed research will assist the researchers, entrepreneurs and farmers to understand the current scenario of food wastage at different stages of the supply chain better. It will provide the guidelines for calculation and mitigation of various stated PHSC losses. This study will be helpful to enhance food availability and food security in post-coronavirus crisis.

Originality/value

The paper explores and highlights PHSC loss calculations and mitigation strategies to identify the postharvest loss situation and better utilization of fresh produces.

smAvo and smaTo: A fruity odyssey of smart sensor platforms in Southern Africa

Avocado and tomato production are key agricultural sectors for many economies including South Africa. The quality of avocadoes and tomatoes that reach consumers is directly dependent on the handling at the postharvest stage. The fruit undergoes an extensive journey, and subsequently stress, comprised of several steps, including harvesting, application of postharvest treatments, packaging and transportation by road and sea to reach the export markets. To date, the quantification of these external stresses on a discrete fruit has not been measured in detail, primarily due to a lack of compatible instrumentation. This paper demonstrates a low cost, stand-alone, open source data acquisition system, termed smAvo and smaTo, that can be introduced effortlessly to monitor agricultural processing facilities and transportation networks. The miniaturised Arduino sensor platform is enclosed within a waterproof enclosure and surrounded by a 3D printed shell manufactured from morphologically compatible materials. The software is customisable to the needs of the research project or individual transportation phases under study, providing both extensive environmental data and high-frequency tri-axis acceleration measurements that are crucial to understanding the dynamic processes that directly affect the final quality of the fruit. Four successful field trials demonstrate the fidelity of both the smAvo and smaTo platforms.

Impact Injury at Harvest Promotes Body Rots in ‘Hass’ Avocado Fruit upon Ripening

Global demand for avocados has risen rapidly in recent years, yet supplying fruit that consistently meets consumer expectations for quality remains a challenge in the industry. Body rots in avocado fruit are a leading cause of consumer dissatisfaction. Anecdotal evidence suggests that body rot development may be promoted by mechanical injury at harvest and packing, despite the fruit being hard, green and mature (i.e., unripe) at these stages. Here, ‘Hass’ avocado fruit, harvested across multiple fruiting seasons from commercial orchards, were subjected to controlled impact from drop heights of 15–60 cm at the time of harvest or packing. With increasing drop height, body rot development at eating ripe stage generally occurred more frequently and produced larger lesions at the impact site and, in some experiments, elsewhere on the fruit. These findings refute a general belief that green mature avocado fruit can tolerate a degree of rough physical handling without ripe fruit quality being compromised. Ideally, best avocado harvesting and packing practice should recognize that unripe fruit must not experience drop heights of 30 cm or higher.

Life cycle environmental impacts of fruits consumption in the UK

Fruits are indispensable for a balanced and healthy diet. However, their environmental impacts remain largely unknown. Using a life cycle approach, this work estimates for the first time the impacts of fruits consumed in the UK. What makes the UK a particularly interesting case is that only 7% of fruits are produced domestically, with the rest imported, largely (70%) from outside of Europe. In total, 21 types of fruit and 46 fresh and processed products produced in the UK and abroad are considered to estimate the impacts at both the product and the national levels. The findings at the product level suggest that melons have the lowest and mangoes and avocados the highest impacts as a significant portion of the last two is air-freighted. Processing leads to high impacts of fruit juices, dried and frozen products. Storage has a considerable contribution to the impacts for fruits stored over a long period, such as apples. Packaging used for canned fruits and juices is also a significant contributor to the impacts. Taking the annual consumption into account, the whole UK fruit sector generates 7.9 Mt CO₂ eq. and consumes 94 PJ of primary energy. This is equivalent to 4% of the annual GHG emissions and 9% of energy demand of the whole UK food sector. Moreover, fruits require 0.35 Mha of agricultural land and 315 Mm³ eq. of water per year. Oranges, bananas and apples are responsible for more than half of the impacts at the national level as they account for 64% of the total fruit consumption in the UK. It is expected that the results of this study will be of interest to different supply chain actors, including farmers, food processors and consumers, aiding them in reducing the environmental impacts of fruits.

Role of biological control agents and physical treatments in maintaining the quality of fresh and minimally-processed fruit and vegetables

Fruit and vegetables are an important part of human diets and provide multiple health benefits. However, due to the short shelf-life of fresh and minimally-processed fruit and vegetables, significant losses occur throughout the food distribution chain. Shelf-life extension requires preserving both the quality and safety of food products. The quality of fruit and vegetables, either fresh or fresh-cut, depends on many factors and can be determined by analytical or sensory evaluation methods. Among the various technologies used to maintain the quality and increase shelf-life of fresh and minimally-processed fruit and vegetables, biological control is a promising approach. Biological control refers to postharvest control of pathogens using microbial cultures. With respect to application of biological control for increasing the shelf-life of food, the term biopreservation is favored, although the approach is identical. The methods for screening and development of biocontrol agents differ greatly according to their intended application, but the efficacy of all current approaches following scale-up to commercial conditions is recognized as insufficient. The combination of biological and physical methods to maintain quality has the potential to overcome the limitations of current approaches. This review compares biocontrol and biopreservation approaches, alone and in combination with physical methods. The recent increase in the use of meta-omics approaches and other innovative technologies, has led to the emergence of new strategies to increase the shelf-life of fruit and vegetables, which are also discussed herein.

Primary Metabolism in Avocado Fruit

Avocado (Persea americana Mill) is rich in a variety of essential nutrients and phytochemicals; thus, consumption has drastically increased in the last 10 years. Avocado unlike other fruit is characterized by oil accumulation during growth and development and presents a unique carbohydrate pattern. There are few previous and current studies related to primary metabolism. The fruit is also quite unique since it contains large amounts of C7 sugars (mannoheptulose and perseitol) acting as transportable and storage sugars and as potential regulators of fruit ripening. These C7 sugars play a central role during fruit growth and development, but still confirmation is needed regarding the biosynthetic routes and the physiological function during growth and development of avocado fruit. Relatively recent transcriptome studies on avocado mesocarp during development and ripening have revealed that most of the oil is synthesized during early stages of development and that oil synthesis is halted when the fruit is harvested (pre-climacteric stage). Most of the oil is accumulated in the form of triacylglycerol (TAG) representing 60-70% in dry basis of the mesocarp tissue. During early stages of fruit development, high expression of transcripts related to fatty acid and TAG biosynthesis has been reported and downregulation of same genes in more advanced stages but without cessation of the process until harvest. The increased expression of fatty acid key genes and regulators such as PaWRI1, PaACP4-2, and PapPK-β-1 has also been reported to be consistent with the total fatty acid increase and fatty acid composition during avocado fruit development. During postharvest, there is minimal change in the fatty acid composition of the fruit. Almost inexistent information regarding the role of organic acid and amino acid metabolism during growth, development, and ripening of avocado is available. Cell wall metabolism understanding in avocado, even though crucial in terms of fruit quality, still presents severe gaps regarding the interactions between cell wall remodeling, fruit development, and postharvest modifications.

Cold shock treatment extends shelf life of naturally ripened or ethylene-ripened avocado fruits

Avocado is an important tropical fruit with high commercial value, but has a relatively short storage life. In this study, the effects of cold shock treatment (CST) on shelf life of naturally ripened and ethylene-ripened avocado fruits were investigated. Fruits were immersed in ice water for 30 min, then subjected to natural or ethylene-induced ripening. Fruit color; firmness; respiration rate; ethylene production; and the activities of polygalacturonase (PG), pectin methylesterase (PME), and endo-β-1,4-glucanase were measured. Immersion in ice water for 30 min effectively delayed ripening-associated processes, including peel discoloration, pulp softening, respiration rate, and ethylene production during shelf life. The delay in fruit softening by CST was associated with decreased PG and endo-β-1,4-glucanase activities, but not PME activity. This method could potentially be a useful postharvest technology to extend shelf life of avocado fruits.

Epidemiology, pathology and identification of Colletotrichum including a novel species associated with avocado (Persea americana) anthracnose in Israel

Anthracnose disease caused by Colletotrichum species is a major constraint for the shelf-life and marketability of avocado fruits. To date, only C. gloeosporioides sensu lato and C. aenigma have been reported as pathogens affecting avocado in Israel. This study was conducted to identify and characterize Colletotrichum species associated with avocado anthracnose and to determine their survival on different host-structures in Israel. The pathogen survived and over-wintered mainly on fresh and dry leaves, as well as fresh twigs in the orchard. A collection of 538 Colletotrichum isolates used in this study was initially characterized based on morphology and banding patterns generated according to arbitrarily primed PCR to assess the genetic diversity of the fungal populations. Thereafter, based on multi-locus phylogenetic analyses involving combinations of ITS, act, ApMat, cal, chs1, gapdh, gs, his3, tub2 gene/markers; eight previously described species (C. aenigma, C. alienum, C. fructicola, C. gloeosporioides sensu stricto, C. karstii, C. nupharicola, C. siamense, C. theobromicola) and a novel species (C. perseae) were identified, as avocado anthracnose pathogens in Israel; and reconfirmed after pathogenicity assays. Colletotrichum perseae sp. nov. and teleomorph of C. aenigma are described along with comprehensive morphological descriptions and illustrations, for the first time in this study.

Control of anthracnose disease via increased activity of defence related enzymes in 'Hass' avocado fruit treated with methyl jasmonate and methyl salicylate

Development of anthracnose disease caused by Colletotrichum gloeosporioides Penz. is one of the major issues within the avocado supply chain. Exposure to methyl jasmonate (MeJA) and methyl salicylate (MeSA) vapours at 10 and 100µmoll^-1 was investigated as an alternative solution to commercial fungicide - prochloraz® that is currently being used by the industry. The incidence of anthracnose disease was found to be significantly reduced in 'Hass' avocado fruit treated with MeJA or MeSA vapours, especially at 100μmoll^-1. The mechanism involved enhanced activity of defence related enzymes, i.e. chitinase, β-1,3-glucanase and PAL, and higher content of epicatechin.

Combined Treatments Reduce Chilling Injury and Maintain Fruit Quality in Avocado Fruit during Cold Quarantine

Quarantine treatment enables export of avocado fruit (Persea americana) to parts of the world that enforce quarantine against fruit fly. The recommended cold-based quarantine treatment (storage at 1.1°C for 14 days) was studied with two commercial avocado cultivars 'Hass' and 'Ettinger' for 2 years. Chilling injuries (CIs) are prevalent in the avocado fruit after cold-quarantine treatment. Hence, we examined the effect of integrating several treatments: modified atmosphere (MA; fruit covered with perforated polyethylene bags), methyl jasmonate (MJ; fruit dipped in 2.5 μM MJ for Hass or 10 μM MJ for Ettinger for 30 s), 1-methylcyclopropene (1-MCP; fruit treated with 300 ppb 1-MCP for 18 h) and low-temperature conditioning (LTC; a gradual decrease in temperature over 3 days) on CI reduction during cold quarantine. Avocado fruit stored at 1°C suffered from severe CI, lipid peroxidation, and increased expression of chilling-responsive genes of fruit peel. The combined therapeutic treatments alleviated CI in cold-quarantined fruit to the level in fruit stored at commercial temperature (5°C). A successful therapeutic treatment was developed to protect 'Hass' and 'Ettinger' avocado fruit during cold quarantine against fruit fly, while maintaining fruit quality. Subsequently, treated fruit stored at 1°C had a longer shelf life and less decay than the fruit stored at 5°C. This therapeutic treatment could potentially enable the export of avocado fruit to all quarantine-enforcing countries. Similar methods might be applicable to other types of fruit that require cold quarantine.