D-limonene (4-isopropenyl-1-methylcyclohexene) is an important compound in several citrus essential oils (such as orange, lemon, tangerine, lime, and grapefruit). It has been used as a flavoring agent and as a food preservative agent, with generally recognized as safe (GRAS) status. D-limonene has been well-studied for its anti-inflammatory, antioxidant, anti-cancer, and antibacterial properties. The antibacterial activity of D-limonene against food-borne pathogens was investigated in this study by preparing a D-limonene nanoemulsion. The D-limonene solution and nanoemulsion have been prepared in six concentrations, 0.04%, 0.08%, 0.1%, 0.2%, 0.4%, and 0.8% (v/v), respectively, and the antibacterial activity was tested against four food-borne pathogens (Staphylococcus aureus, Listeria monocytogenes, Salmonella enterica, and Escherichia coli). The results showed that the D-limonene nanoemulsion had good nanoscale and overall particle size uniformity, and its particle size was about 3~5 nm. It has been found that the D-limonene solution and nanoemulsion have a minimal inhibitory concentration of 0.336 mg/mL, and that they could inhibit the growth of microorganisms efficiently. The data indicate that the D-limonene nanoemulsion has more antibacterial ability against microorganisms than the D-limonene essential oil. After bananas are treated with 1.0% and 1.5% D-limonene nanoemulsion coatings, the water loss of the bananas during storage and the percentage of weight loss are reduced, which can inhibit the activity of pectinase. The application of a biocoating provides a good degree of antibacterial activity and air and moisture barrier properties, which help with extending the shelf life of bananas.

Papaya (Carica papaya L.) is a climacteric fruit, and its quality will rapidly decrease after ripening. Hence, the storage life of its fruit is short. D-limonene is a terpene compound in citrus essential oil and has antibacterial and antioxidant properties. The addition of D-limonene in edible coating can delay volatilization, prevent microorganism and pathogen invasion, decrease water loss, inhibit softening, decrease gas exchange, and extend the storage life of fruits. In this study, 0.25%, 0.5%, and 1% D-limonene nanoemulsion coatings were used for post-harvest immersion treatment of “Tainung No. 2” papayas and its effects on appearance, chlorophyll content, respiration rate, ethylene production, pectin methylesterase, polygalacturonase activity, decay loss, firmness, total soluble solid, titratable acidity, ascorbic acid, and total plate count were investigated. After the papayas were treated with 0.5% D-limonene nanoemulsion coating, polygalacturonase and pectin methylesterase activities decreased, fruit firmness was maintained, and ascorbic acid content was high. On the last day of storage, polygalacturonase and pectin methylesterase activities were 0.01 and 0.02 U/kg FW lower than the control group, respectively; firmness was higher than the control group by 1.75 N, and ascorbic acid content was higher than the control group by 31.97 mg/100 g FW. On Day 2, the treatment showed delay in total soluble solid accumulation and chlorophyll degradation, consequently delaying the color change in fruits. The coating decreased decay loss by 40% on Day 2, decreased respiration rate by 97.0 mg CO₂ kg⁻¹ h⁻¹, and ethylene production by 5.7 µL kg⁻¹ h⁻¹ on Day 2. Simultaneously, the coating decreased the total plate count and resulted in a good appearance. Fruits coated with a 1% D-limonene nanoemulsion coating showed defects in color change. In summary, 0.5% D-limonene nanoemulsion coating delayed “Tainung No. 2” papaya ripening and decreased microbial infection, consequently extending its storage life.

Atemoya (Annona squamosa x A. cherimola hybrid) is a typical climacteric fruit that has a high respiration rate after harvest, short storage life, and is highly susceptible to fruit cracking and rot. Therefore, this study was intended to apply D-limonene nanoemulsion coating on fruit to prolong the storage life, reduce spoilage, and facilitate the expansion of the market. Green mature atemoya fruit coated with different concentrations of D-limonene nanoemulsion (0.25%, 0.5%, 1.0%, 1.5%, and control) was stored in a 14°C refrigerator for relevant analysis and investigation. The results showed that the use of 0.25% D-limonene nanoemulsion inhibited the browning on the fruit surface, and reduced physiological metabolisms. The browning phenomenon on the fruit surface increased as the D-limonene concentration ratio increases. Since the high concentration caused damage to the peel cells, 0.25% D-limonene was chosen as optimum for atemoya coating. The fruit of atemoya maintained green peel color (L × 28.6, a × 6.63, b × 12.3) after storage at 14°C for 21 days with 0.25% D-limonene nanoemulsion coating. At the same time, after 0.2% D-limonene nanoemulsion coating, the weight loss rate was about % less than that of the control group (0.25% treatment was 11.3%; control was 14.2%) and high pectin content (0.25% treatment was 16.9 mg AGA g⁻¹AIS⁻¹; control was 9.89 mg AGA g⁻¹AIS⁻¹). Coating of D-limonene nanoemulsion can reduce the physiological response of atemoya fruits after harvesting, prolong the storage time, and increase the feasibility of their export. From the experimental results, D-limonene showed the potential to be widely used in fruit preservation agents in the future.

Winged beans accumulate abundant field heat following harvest, and their shelf life is shortened if precooling is not performed promptly. In the present study, top-suction forced-air precooling (FC) was employed to rapidly remove field heat from pods, and its effects on winged bean pod storage quality and shelf life were assessed. After postharvest FC to remove field heat from winged bean pods, the mean 1/2 precooling time was 5.8 min and 7/8 precooling time was 14.7 min, which was 9.6 times and 11.7 times faster than room cooling (RC), respectively. Moreover, after FC was applied to remove field heat, the weight loss rate at 7/8 precooling time was 0.92%, significantly lower than that after RC was applied (1.98%). FC could delay decay, and the decay rate was only 18% on day 14 storage, which was lower than 52% of RC. During 12 °C and 85% relative humidity (RH) storage, the shelf life of winged bean pods in the FC group was 14.8 days, which was significantly longer than that of the pods in the RC group (10.6 days). In conclusion, FC is an effective precooling method to rapidly remove field heat postharvest and maintain the storage quality of winged beans.