Five Significant Postharvest Fruit Analysis Research Findings in 2023

• Research focuses on finding alternatives to safe chemicals for people and the environment to enhance postharvest quality.
• The studies also consider the impact of soil-less and greenhouse cultivation on fresh produce quality.
• Scientists are addressing gene expression and antioxidant action that regulates physiology in postharvest quality and injury response.
• The standard quality parameters used to estimate quality are dry matter, total soluble solids, titrable acidity, firmness, and color.

Before reaching consumers, around 20–50 percent of fresh produce is lost in postharvest processes. These losses occur in all production and postharvest stages, including handling, packaging, storage, and transport. Losses occur due to quality deterioration, microbial spoilage, and senescence. Various strategies are used to limit these losses by targeting the causes. Explore these five fruit analysis research findings in 2023 that consider local conditions to design solutions to reduce fresh produce waste.

1. Production and Packaging Methods to Improve Postharvest Cucumber Quality

Cucumbers are the second most-grown vegetable; global production was around 119.2 million tonnes in 2021.

In cucumbers, weather like temperature and solar radiation levels, cultivation practices like fertilization and irrigation, and transport and storage conditions matter for quality.

The substrate and artificial lighting can also influence cucumber quality in hydroponics, where plants are grown year-round. Mineral wool is the standard substrate in hydroponic conditions, but biodegradable and more environment-friendly alternatives are in demand. Lignite is a popular alternative. However, there was no information on its effect on cucumber quality during postharvest storage.

A study by Łaźny et al. 2023, on the effects of growing conditions, such as lignite substrates and assimilation lighting, in hydroponic cultivation, as well as storage methods on the quality and postharvest shelf life of greenhouse cucumber fruit, was conducted to address the demand for high-quality cucumber fruit throughout the year.

Experiment

The experiment covered the following steps:

• Cucumber plants were grown in lignite and mineral wool mats for comparison. Sodium and LED lamps provided sunlight supplementation.
• For five days, packaging material trials for postharvest cold storage included plastic crates, plastic bags, and cardboard crates.
• Trading conditions simulation were for 10 days: five days of cold storage and five days at 22ᵒC.
• Quality parameters tested after cold storage and ten days of transport were sensory attributes, fruit dry matter content, total soluble solids (TSS), hardness, and nitrate content of cucumbers.

Key findings and conclusions from the study are as follows:

• Growing Conditions Impact on Fruit Quality: Cucumber fruit grown in lignite substrate exhibited lower weight loss during storage. Fruit from lignite substrate had higher TSS and dry matter content than those from mineral wool substrate. Lignite-grown fruit had lower nitrate content.
• Effect of Lighting and Substrate on Sensory Parameters: Fruit from plants grown in lignite substrate under LED lighting showed the best sensory parameters.
• Storage and Packaging Influence on Weight Loss: PE film packaging reduced fruit weight loss during transport and storage. Fruit packed in foil showed extended shelf life and improved postharvest quality. Cucumbers stored in cardboard boxes suffered weight loss more slowly than in other materials.
• Overall Impact of Production Choices: Organic lignite substrate and LED supplementary lighting positively affect greenhouse cucumber fruit’s quality and postharvest shelf life.
• Recommendations for Prolonging Postharvest Quality: Proper packaging, transport, and storage are essential for prolonging postharvest quality. Fruit removed from PE film and placed in a cardboard box exhibited slower weight loss.

The study suggests that combining strategic choices in production methods, including using organic lignite substrate and LED lighting, can significantly enhance the quality and shelf life of hydroponically grown cucumber fruit. Additionally, carefully considering packaging materials and methods can further contribute to maintaining postharvest quality.

2. Calcium Chloride Improves Postharvest Pepper Color and Texture

Figure 1: “Gene network regulatory model of mechanically injured green pepper (A) without treatment and (B) treated with CaCl2 during storage. Compared with CK-0, the red arrow means up-regulated, the green arrow means down-regulated, the pink arrow means up-regulated slightly, and the light green arrow means down-regulated slightly,” Ma et al., 2023. (Image credits: https://doi.org/10.1016/j.postharvbio.2023.112437)

Green pepper (Capsicum annuum L.) is a vegetable popular for its bright color, flavor, and crisp texture. It is also rich in sugar, organic acids, protein, vitamins, and other nutrients. The antioxidant capsaicin has several health benefits for people. However, its thin skin and hollow fruit structure make it vulnerable to vibration, impact, and compression damage during postharvest handling and storage stages.

Injuries trigger physiological and biochemical changes that spoil appearance, leading to microbial infection, loss of edibility and nutrition, and decay. To prevent economic losses through postharvest quality deterioration, a study by Ma et al. 2023 tried calcium chloride (CaCl2) treatment, a cost-effective method. Calcium is an essential cell wall and membrane component that maintains integrity and strength. It also reduces bruising, browning, ripening, and senescence rate. The US Food and Drug Administration (FDA) has classified CaCl2 as a safe salt.

Experiment

Calcium chloride’s effect as the preharvest treatment on improving postharvest quality is established; however, its ability to limit mechanical damage results has not been studied. Ma et al. 2023, examined the effect of CaCl2 on the physiological quality and the gene expression regulatory mechanisms involved through metabolome, transcriptome, and ATAC-seq (Assay for Transposase Accessible Chromatin with high-throughput sequencing) analysis.

The quality parameters tested were sensory quality, including the color and hardness of the fruits.

Key findings and conclusions from the study included:

• Inhibition of Redness and MDA Elevation: The treatment with calcium inhibited the development of redness in the fruit. A decrease in the malondialdehyde (MDA) level suggests a reduction in oxidative stress.
• Gene regulatory mechanisms test findings showed the following results:
• Transcriptomics revealed effects on the expression of key genes related to various processes, including fruit color change, fruit softening, active oxygen metabolism, and hormone response.
• Metabolomics identified changes in metabolite concentrations.
• ATAC-seq provided information on chromatin accessibility changes.
• Construction of Regulatory Network Model: A regulatory network model of calcium treatment on postharvest mechanical injury of green pepper fruit was developed based on the observed effects. This model illustrates that CaCl2 decreased carotenoid accumulation, reduced cell wall degradation, and improved antioxidant activity of ROS removal, see Figure 1.

The study provides valuable insights into the impact of mechanical injury on fruit after harvest. The research contributes to understanding the molecular and physiological changes in green pepper fruit postharvest, highlighting the potential benefits of calcium treatment. The treatment alleviates the adverse effects of postharvest mechanical damage by maintaining sensory quality color, preventing red color development, and retaining the hardness of green pepper fruit.

3. Zero Energy Cool Chamber and Plastic Packaging Retain Mango Quality

Figure 2: The static cooling principle of Zero Energy Cool Chamber (ZECC), Niel Noble. (Image credits: https://srrweb.cc.lehigh.edu/app/ZECC)

While cold storage is the accepted method to reduce food loss, it is expensive and needs constant and reliable electricity. Zero Energy Cool Chamber (ZECC) provides an eco-friendly storage system for hot, arid climates. It doesn’t require electricity. Moist sand between double brick walls is reduced to remove the heat and keep the central storage space cool through passive evaporative cooling, see Figure 2.

In Indonesia, Dewitara et al. 2023, tested the efficacy of ZECC and two packaging materials in maintaining mango quality and improving shelf-life.

Mango production is increasing since mango is a local fruit that is highly nutritious. However, the fruits are prone to bruising because improper postharvest handling can reduce quality and shelf-life.

Experiment

The mango cultivar tested was Golek, and the experiment was conducted in two stages between January and March 2021. The two packaging materials tested were low-density polyethylene (LDPE) and LDPE with perforations.

In the first stage, mango physical quality was evaluated and prepared for postharvest storage by washing and packing in LDPE and LDPE with perforations stored for 18 and 15 days at ZECC temperature (±26 °C).

In the second stage, mango quality was tested after storage.

The quality parameters tested were sensory (aroma, texture, and taste), skin color, weight loss, firmness, total acid, TSS, pH, water content, and vitamin C.

Key findings and conclusions from the study are listed below:

• LDPE packaging stored for 18 days: LDPE retained various qualities, including vitamin C, total acid, TSS, pH, water content, skin color (L* and b*), and sensory attributes.
• Perforated LDPE packaging stored for 15 days: Perforated LDPE retained TSS, L* and b* color, water content, organoleptic color, aroma, texture, and taste.

This study shows that LDPE and perforated LDPE packaging showed different preservation capabilities for various qualities of mangoes. It provides insights into the impact of packaging on the postharvest quality of mangoes and the effectiveness of varying packaging methods in combination with the ZEEC storage conditions.

4. Melatonin Treatment Reduces Infection and Increases Strawberry Shelf Life

Figure 3: Graphic abstract of the experiment, Promyou et al. 2023. (Image credits: https://doi.org/10.3390/foods12071445

Strawberries (Fragaria × ananassa cv. Camino Real) are the USA’s third most important agricultural product and the fifth most consumed fruit.

A non-climacteric fruit, strawberry postharvest quality is most threatened by Botrytis cinerea, which causes the gray mold disease. The mold leads to losses of 25-30% of strawberries annually. Several chemicals have been used to contain the gray mold damage, but health and environmental safety issues have renewed research efforts to find safer, environmentally friendly alternatives.

Promyou et al. 2023, tested the suitability of exogenous melatonin (MT) treatment to control the gray mold and the resultant strawberry quality.

Experiment

Strawberries from a Louisiana orchard plucked at 80% ripeness were harvested and taken to the laboratory within an hour.

The fruits were inoculated with B. cinerea, treated with 100 µM MT, and compared with two controls inoculation and 5% sodium hypochlorite treatment. Another set was given MT treatment without inoculation. After inoculation, the fruits were stored at room temperature (25 ± 2°C) and 80-85% relative humidity for six days.

The fruits were examined every two days for quality parameters like fruit color, firmness, TSS, titrable acidity, and weight loss, antioxidant enzyme activities, and 2,2-diphenyl-1-picrylhydrazyl (DPPH) scavenging capacity,

Key findings and conclusions from the study are as follows:

• Color Maintenance: The immersion of strawberry fruit in the melatonin solution effectively maintained the brightness of the fruit and delayed the natural change in fruit color.
• Acidity and TSS: Melatonin treatment helped maintain the titratable acidity level in the strawberries, slowed the increase of TSS, and kept the fruit’s taste and flavor.
• Fresh Weight and Firmness: Strawberries treated with melatonin retained their fresh weight and fruit firmness, indicating that melatonin might play a role in preserving the physical attributes of the fruit.
• Disease Resistance: The melatonin-treated strawberries showed reduced infection by the fungus cinerea compared to untreated control fruit and fruit treated with 5% sodium hypochlorite (NaOCl).
• Antioxidant Capacity: Melatonin treatment increased the accumulation of DPPH (2,2-diphenyl-1-picrylhydrazyl) scavenging capacity, indicating enhanced antioxidant activity. Additionally, the activity of antioxidant enzymes such as superoxide dismutase (SOD), peroxidase (POD), and ascorbate peroxidase (APX) was increased, except for catalase (CAT). So, melatonin contributes to the fruit’s defense against oxidative stress.
• Effect on cinerea Inoculation: Even when the strawberries treated with melatonin were inoculated with B. cinerea, the positive effects on postharvest quality were maintained. It indicates that melatonin could effectively preserve the quality of strawberries even in the presence of fungal infection.

In summary, the study shows that the exogenous application of melatonin could be a promising strategy to enhance the postharvest quality of strawberries by preserving color, acidity, firmness, and antioxidant capacity while reducing susceptibility to fungal infections like B. cinerea, see Figure 3.

5. Isothermal Storage Delays Apple Senescence

Figure 4: Graphical abstract of the experiment, Chen et al. 2023. (Image credits: https://doi.org/10.3390/foods12091765)

Temperature fluctuations (TF) significantly affect fruit quality and senescence since every 10°C difference can increase the physiological rate by 2-3 times, changing fruit quality. Relative humidity is also crucial, as it and temperature can boost infections.

A study by Chen et al. 2023, studied if cooling and isothermal can improve fresh produce quality in apples by maintaining physiological rates.

Experiment

Three sets of freshly harvested apples were stored at 85–90% relative humidity for 60 days at TF of 5 ± 5°C and 5 ± 1°C and isothermal or constant temperature (CT) at (5 ± 0.1°C).

Fruits were tested every ten days for firmness, TSS, TA, weightless electrolyte leakage (EL), respiration rate, and antioxidant activities.

Key findings and conclusions from the study include the following:

• Quality Attributes: Apples in the CT group maintained higher levels of firmness, fresh weight, TSS, and TA compared to the TFs group.
• Respiratory and Stress Parameters: Apples in the CT group exhibited a suppressed respiration rate and lower levels of electrolyte leakage (EL), malondialdehyde, superoxide anion (O2·−), and hydrogen peroxide accumulation.
• Enzymatic and Biochemical Activities: The activities of antioxidant enzymes, including superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), and glutathione reductase (GR), were higher in the CT group, indicating a more robust antioxidant defense system. At the end of storage, the CT group showed significantly higher activities of SOD, CAT, APX, and GR compared to the TF5 group.

Higher levels of ascorbic acid (AsA), reduced glutathione (GSH), total phenols, and total flavonoids were observed in apples stored in the CT environment.

• Energy Status: Apples in the CT group maintained higher adenosine triphosphate (ATP) content and exhibited increased activities of H+-ATPase, Ca2+-ATPase, cytochrome c oxidase (CCO), and succinate dehydrogenase (SDH).
• Conclusion: The constant temperature storage environment was associated with retarded fruit senescence. The retardation was attributed to enhanced antioxidant capacities (higher enzyme activities and lower oxidative stress) and the maintenance of a higher energy status in apple fruit.

The findings show that isothermal storage retards fruit senescence. A constant temperature storage environment positively influences the postharvest quality of apples by promoting antioxidant defenses and maintaining cellular energy levels.

Precision Measurement of Parameters for Fruit Analysis Research

Studies that test quality parameters like those discussed above could use the Felix F-750 Produce Quality Meter. Produced by Felix Instruments Applied Food Science, the device that uses Near-infrared spectroscopy and chemometrics is suitable for non-destructive, rapid, and accurate analysis of several quality parameters like dry matter, TSS, titrable acidity, and internal and external color. The tools are helpful in both fields and laboratories. They are also a valuable industry standard in all stages of the food supply chain to monitor and control quality to reduce food waste once findings reach the application phase.

Sources

1. Łaźny, R., Przybył, J. L., Wójcik-Gront, E., Mirgos, M., Kalisz, S., Bella, S., … & Kowalczyk, K. (2023). Effect of lignite substrate and supplementary lighting and packaging type on postharvest storage quality of cucumber fruit. Scientia Horticulturae, 321, 112350.

2. Ma, L., Zheng, Y., Sang, Z., Ge, Y., Bai, C., Fu, A., … & Zuo, J. (2023). Multi-omics analysis reveals the mechanism of calcium-reduced quality deterioration in mechanically injured green pepper fruit. Postharvest Biology and Technology, 204, 112437.

3. Dewitara, S., Dirpan, A., & Rahman, A. N. F. (2023, May). Quality analysis of Golek mango fruit (Mangifera indica L.) on Zero Energy Cool Chamber (ZECC) storage with packaging combination. In AIP Conference Proceedings (Vol. 2596, No. 1). AIP Publishing.

3a. Zero Energy Cooling Chamber. Retrieved from https://srrweb.cc.lehigh.edu/app/ZECC

4. Promyou, S., Raruang, Y., & Chen, Z. Y. (2023). Melatonin Treatment of Strawberry Fruit during Storage Extends Its Postharvest Quality and Reduces Infection Caused by Botrytis cinerea. Foods, 12(7), 1445.

5. Chen, L., Wang, M., Wang, H., Zhou, C., Yuan, J., Li, X., & Pan, Y. (2023). Isothermal Storage Delays the Senescence of Postharvest Apple Fruit through the Regulation of Antioxidant Activity and Energy Metabolism. Foods, 12(9), 1765.