African Journal of Food Science and Technology

Extension of the Shelf-life of Minimal Processed Oyster Mushrooms with Chemical Treatments

Kanagarajah Premakumar^1*, Sritharan Sahana² and M. A. Prathibha Malmi Perera^{1 1}Department of Agricultural Chemistry, Eastern University, Chenkalady, Sri Lanka
²Department of Biosystems Technology, Eastern University, Chenkalady, Sri Lanka
^*Corresponding Author:
Kanagarajah Premakumar, Department of Agricultural Chemistry, Eastern University, Chenkalady, Sri Lanka, Tel: 0776073384, Email: premakumar.k2016@gmail.com

Received: 13-Jul-2020 Published: 24-Sep-2020, DOI: 10.14303/ajfst.2020.011

Introduction

Sri Lanka needs a continuous supply of good quality, locally cultivated mushrooms. Pleurotus ostreatus (Oyster mushroom) is well preferred vegetable for Sri Lankans and as an ingredient in soup because of its high nutritive content, unique flavor, and medicinal properties. Many varieties of mushrooms are consumed throughout the world because of their medicinal properties attributed to their bioactive compounds that present immune modulating, antitumor, antioxidant, radical scavenging, cardiovascular, antibacterial, antiviral, and antihypertensive, ant hypercholesterolemia, detoxification, hepatoprotective, and antidiabetic activities. (Rathee et al., 2012).

The Pleurotus genus stands out because of its nutritional composition (0.8-2 g proteins, including 16 different essential amino acids, vitamins, folic acid, minerals, carbohydrates, lipids and a low-calorie content). This composition gives it functional properties, enabling it to be used in treating diseases like hypertension, and it also exhibits antitumoral, anticancer and antiviral activities (Caglarirmak, 2007). These characteristics have increased its demand and consumption in presentations such as frozen, dehydrated, precooked, fresh as a whole product and minimally processed (Carrera et al., 2007). Minimally processed products are an important alternative to encourage consumption of oyster mushrooms. They can be prepared by one or more-unit operations, including sliced or diced products. Preservation treatments include the use of minimal heating, chemical preservatives, radiation, pH control, immersion in chlorinated or electrolyte water, modified atmosphere packaging and maintaining a suitable temperature during a cold chain (2-7 ˚C) (Correa et al., 2016).

Also, fresh mushroom is susceptible for microbial growth due to their high-water activity, high respiration rate, and neutral pH (Carrera et al., 1998) and continuous metabolism after harvest which results in changes in some of its quality parameters such as color, weight, and texture (Okhuoya, 2005). These characteristics limit the postharvest shelf life of fresh mushroom to few days (1–3 days) which is an impediment to their distribution and storage (Ares et al., 2007), hence there is a need of a technology that can be used to preserve the postharvest quality of mushroom while ensuring its safety. Food-grade chemical preservatives such as ascorbic acid, calcium chloride, sodium metabisulfite solution and citric acid have been used within their maximum permissible levels to prolong the shelf life of foods. The aim of this study was to evaluate the effect of ascorbic acid, calcium chloride, sodium metabisulfite solution and citric acid on minimal processing and select chemical preservative(s) that are suitable for extending the shelf life of oyster mushroom.

Materials and Methods

This study was undertaken at the Food Science Laboratory of the Department of Agricultural Chemistry, Faculty of Agriculture, and Eastern University, Sri Lanka for a period of five months from January to May 2019.

Raw materials

Undamaged, healthy, sound fresh oyster mushrooms (Pleurotus spp.) were harvested under normal commercial conditions from a commercial farm at Mylambaveli, Batticaloa district. Harvested mushrooms were kept on plastic crates and transported to the laboratory. Mushrooms were sorted by size and appearance. Diseased, damaged, and extremely large or small mushrooms were discarded to minimize biological variability. Citric acid, ascorbic acid, calcium chloride, sodium metabisulfite and other all the materials were collected from Food Science Laboratory, Department of Agriculture Chemistry, Eastern University, Sri Lanka.

Experimental design

The experiment was laid out in a Completely Randomize Design (CRD). Experiment has four treatments with three replications. Treatments were experimented with minimal processing and divided and soaked in three types of chemical solutions for one minute. As soon as they soaked, those were taken out to avoid water-soaked appearance. After that, mushrooms were dried in air to reduce moisture content to prevent microbial growth. Finally, four treatments of air-dried mushrooms were packed in macro perforated polythene bags. Oyster mushrooms packed in macro perforated polythene bags without soaking in any chemical solution considered as T1, oyster mushrooms packed in macro perforated polythene bags after soaking in citric acid solution as T2, oyster mushrooms packed in macro perforated polythene bags after soaking in ascorbic acid and calcium chloride solution as T3, and oyster mushrooms packed in macro perforated polythene bags after soaking in sodium metabisulfite solution as T4. Then the packets were labeled and stored in refrigerator.

Nutritional analysis

All the physico- chemical parameters were analyzed using the recommended AOAC (2002) methods. Moisture content, ash content, pH, protein content, total carbohydrate, Fat, Dietary fiber were analyzed after formulation and the storage period.

Organoleptic qualities analysis

The color, taste, texture, aroma and overall acceptability were evaluated using a Seven –point hedonic scale after formulation.

Storage studies

The four treatments of freshly prepared Minimally Processed Mushrooms samples were subjected for storage studies. They were stored in refrigerator at 4˚C for two weeks period of time. Physico- chemical analysis of the above samples was done at 3 days intervals. Sensory evaluation was done to curry samples prepared from the minimally processed mushrooms stored in a refrigerator for period of 12 days using seven-point hedonic scales after two weeks to evaluate color, taste, texture, aroma and overall acceptability,

Conclusion

Minimally processed treated with sodium metabisulfite oyster mushroom is the best for maintaining the physicochemical and Organoleptic qualities with an extended shelf life, which has no harmful effects for consumers. Even though permissive levels of sodium Meta bisulfate (400ppm) are recommended as people with asthma have a greater chance of having an allergic reaction to sodium metabisulfite. Minimally processed oyster mushroom is a new product for improving the storage capacity of mushrooms. Minimal processing enhanced the shelf life of mushrooms, reduced the post-harvest losses and reduces the perishability & deterioration rate of mushrooms. Because of their fresh nature, minimally processed mushrooms provide convenience to the user.

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