Food browning is undesirable as it causes deterioration in food quality and appearance. This phenomenon was related to polyphenol oxidase (PPO), which catalyzes conversion of phenolic compounds into -quinones. The present work evaluated the use of chemical and natural anti-browning agents to prevent the browning of ginger PPO. Sodium metabisulfite (5 mM) is a better chemical inhibitor compared to l-cysteine and sodium chloride as 55.00% of ginger PPO inhibition was achieved. The percentage of inhibition increased as the concentration of anti-browning agents increases. The addition of heated onion, chili pepper and pineapple extracts exhibited a stronger inhibitory effect on ginger PPO than unheated extracts. Heated chili pepper extract was the best natural inhibitor found in this study and it inhibited the ginger PPO (47.97%) mixed-competitively. Natural anti-browning agents have potential to be used to control the browning of ginger as well as other vegetables and fruits.

Honey, pineapple, chilli pepper, and onion extracts were investigated for their ability to inhibit enzymatic browning in sweet potatoes. Honey had the highest inhibition (41.39%–48.0%), comparable with l‐ascorbic acid. Heated onion extract increased polyphenol oxidase (PPO) inhibition by 2.5‐fold when 4‐methylcatechol was used as substrate. However, percentage inhibition decreased drastically (7.42%–19.67%) when heated pineapple extract was used. Fresh chilli pepper extract showed a higher PPO inhibition (45.97%) than that of heated extract. These natural inhibitors were also compared to synthetic inhibitors that ranked: l‐cysteine > l‐ascorbic acid > sodium chloride. l‐cysteine was the most effective chemical inhibitor which inhibited up to 70.4% PPO activity. It was found that natural inhibitors extracted from common food items are able to control the enzymatic browning of sweet potato. These natural inhibitors extracts are safe to human and would also be potentially replaced chemical inhibitors for the preservation of other fruits as well as vegetables. Practical applicationsFruits and vegetables are prone to enzymatic browning. This is caused by the oxidation reaction of endogenous phenolic compounds, catalyzed by PPO. PPO oxidizes o‐diphenols to o‐quinones, which will turn into brown pigments as the o‐quinones polymerize immediately. Enzymatic browning of fruits and vegetables always take places after harvest, during the post‐harvest processing as well as storage. Thus, identification of suitable and acceptable inhibitors is important in order to prevent food browning and to increase the food marketability for food industry. This study indicated that sweet potato PPO was successfully inhibited by extracts from common food items such as honey, chilli pepper, pineapple, and onion which are safe for human consumption. Thus, these natural inhibitors could also be applied to similar food materials such as apples, star‐fruit, and normal potatoes. We expect that the inhibitors examined in this study can be isolated and identified as lead molecules for the development of natural anti‐browning food additives.

Sapodilla puree was naturally viscous and was liquefied with enzymes (Pectinex Ultra SP‐L and Celluclast 1.5L) acting individually or in combinations at varying concentrations (0.5–2.5% v/w), times (0.5–2.5 h) and temperatures (35–55C) prior to the drying process. Treatment with enzymes in combinations showed greater effect in reducing viscosity (90.0–96.1%) as compared to single enzyme treatment (22.1–59.1%). Best condition chosen was 0.5% (v/w) from each Pectinex Ultra SP‐L and Celluclast 1.5 L at 40C for 1.5 h, which required minimal processing cost. During spray drying, liquefied puree was added with different maltodextrin (DE of 10–12) concentrations (10–50% w/v) at varying inlet temperatures (140–220C). The results indicated that the powder being spray‐dried at 180C with 30% (w/v) added maltodextrin had high product yield (57.42%) with acceptable qualities in terms of moisture content, hygroscopicity, bulk density, solubility and water activity. The produced sapodilla powder could potentially be incorporated in various food products to diversify in the market. Practical Applications The intake of fruits is highly beneficial to health. However, most fruits have short shelf life because of their high sugar and water contents. As a result, many fruits are wasted without proper processing. Therefore, a solution is sought to solve this problem. The preservation method through spray drying is highly recommended due to the quick and large throughput moisture evaporation. It is economically cheap, flexible and the equipment used is readily available. Moreover, it is best in preserving heat‐sensitive products. The fruit powder produced presents great potential as a source of functional food additive such as flavoring and coloring agents in various food products, thus providing a wide variety of interesting experience for consumers. However, it is not easy to spray‐dry the fruit into powder because of the stickiness problem. Most samples tend to stick to the wall of the drying chamber, thus ending up having a low product yield. This study strives to provide detailed knowledge on solving the wall deposition problem through the use of enzyme liquefaction method. It also presents details about the quality of powder produced at different drying conditions.

Banana pulp was treated with Pectinex Ultra SP‐L and Celluclast 1.5 L individually or in combinations at different concentrations (0–2.5% v/w) and incubation times (0–2.5 hr) prior to spray drying process. About 41.12 and 61.27% viscosities reduction were achieved with Celluclast 1.5 L and Pectinex Ultra SP‐L, respectively. Enzymatic liquefaction obtained with combinations of 1.5% (v/w) Pectinex Ultra SP‐L and 1.0% (v/w) Celluclast 1.5 L for 2.5 hr showed the greatest viscosity reduction (88.54%). Liquefied puree was added with 10–50% w/w maltodextrin and spray‐dried at different inlet temperatures (140–180 °C). The results indicated that the highest drying yield (51.50%) was obtained at 150 °C with 30% (w/w) maltodextrin. The obtained powders were analyzed for water activity (0.25 ± 0.01 Aw), moisture content (0.29 ± 0.01%), hygroscopicity (13.58 ± 0.01%), solubility (54.00 ± 1.00 s), color (L* = 91.73 ± 0.05; a* = 0.39 ± 0.01; b* = 7.53 ± 0.04), and bulk density (0.44 ± 0.03 g/ml). The produced powder could potentially be incorporated into other fruit‐based products. Practical applications Tropical fruits are widely cultivated in developing countries as a source of nutrition and revenue. Most of these fruits are high in moisture content (>80%), therefore, they are prone to deterioration and have a shorter shelf life. The amount of fruits spoiled during the harvesting season can be minimized by dehydration method via spray drying to increase their shelf life and to ensure their availability all year round. The resulting spray‐dried powders can potentially be incorporated into various food products as a source of functional food additive such as flavoring or coloring. The detailed knowledge obtained from this study on the best conditions for enzymatic liquefaction to ease the drying process and optimum drying conditions to reduce the stickiness problem for the production of good quality fruit powder. In addition, these parameters can be used as a reference for large scaled production in food industry.

Purification and characterization of polyphenol oxidase (PPO) from Chinese parsley () were achieved. Crude PPO exhibited an enzyme activity of 1,952.24 EU/mL. PPO was partially purified up to 6.52x with a 10.89% yield using gel filtration chromatography. Maximal PPO activity was found at 35°C, pH 8.0 for 4-methylcatechol and at 40°C, pH 7.0 for catechol. PPO showed a higher affinity towards 4-methylcatechol, but a higher thermal stability when reacting with catechol. LCysteine was a better inhibitor than citric acid for reducing PPO activity at concentrations of 1 and 3mM in the presence of either substrate. Two 46 kDa isoenzymes were identified using SDS-PAGE. Isolation and characterization of Chinese parsley serves as a guideline for prediction of enzyme behavior leading to effective prevention of enzymatic browning during processing and storage, including inhibition and inactivation of PPO.