SHELF LIFE AND STORAGE QUALITY OF WHITE BUTTON MUSHROOMS (AGARICUS BISPORUS) AS AFFECTED BY PACKAGING MATERIAL

Neha Singh* 1 , Devina Vaidya 2 , Vigya Mishra 3 and K S Thakur 2 . 1. Warner School of Food and Dairy Technology, SHIATS, Allahabad (UP), India. 2. Department of Food Science and Technology, Dr Y S Parmar UHF, Nauni, Solan (HP), India. 3. Amity International Centre for Post Harvest Technology and Cold Chain ManagementAmity University Uttar Pradesh, Noida (UP), India. ...................................................................................................................... Manuscript Info Abstract ......................... ........................................................................ Manuscript History


Materials and Methods:-
Sample collection:-Fresh picked, unwashed, whole white button mushrooms, used in this study were procured from Mushroom Center, Dr Y S Parmar University of Horticulture and Forestry, Nauni, Solan. After harvesting, they were sorted out for any damage or discolouration, and after it their stems were cut.
Fresh unwashed mushroom was observed to contain 90.20 + 0.03 % of moisture while the average pH value assessed in fresh mushroom was 6.85 + 0.02. The average optical density to measure the degree of whiteness of fruit bodies of unwashed mushroom measured at 420 nm was recorded as 0.610 + 0.01 while the total phenols was recorded as 0.44 + 0.02 %.

Washing treatment:-
The sorted, unwashed mushrooms were given three different washing treatments viz., plain water washing (T 1, control), 0.5 % KMS (T 2 ) and 0.5 % KMS + 0.5 % NaCl + 0.5 % CaCl 2 (T 3 ) for 2 min to remove the adhering casing soil and then placed on the absorbent paper to remove excess surface water.
Packaging and storage:-After the washing treatment mushrooms (about 200+1 g) were packed in four different packaging materials viz., polypropylene bag (PP, 1500 gauze), low density polyethylene bag (LDPE, 200 gauze), commercially used packages (obtained from the market which is commonly used by the local growers and whose thickness was unknown) and paper punnets with shrink wrapping and sealed as shown in Fig. 1. The packed mushrooms were then stored at two different conditions i.e. at ambient (22+2° C) and refrigerated (4+2° C). The mushrooms were then analyzed for various physico-chemical changes and sensory attributes at the interval of 3 days viz., 0, 3, 6, 9 days. Quality Parameters:-Weight loss (%):-Weight loss in mushroom packed in different packaging materials was calculated by deducting the weight of mushroom after storage from the initial weight of mushroom i.e. before storage. The results were expressed as per cent weight loss in mushroom.
Weight loss by mushroom (%) = (Initial weight of sample -Final weight of sample) × 100 Initial weight of sample Moisture content:-The moisture content was estimated by drying the weighed sample (5 g) to a constant weight in hot air oven at 70+2° C. The dried samples were then cooled to room temperature in a desiccator prior to weighing (Ranganna, 2010). Loss in weight of sample after drying representing the moisture content was expressed as per cent (w/w). Moisture content (%) = (Weight of fresh sample -Weight of dried sample) × 100 Weight of fresh sample 1792 Total phenols:-The amount of total phenols in the mushroom sample was determined with the Folin-Ciocalteu reagent using catechol as a standard (Bray and Thorpe, 1954). One gram of sample was taken and grinded with 10 ml of 80 % ethanol in pestle and mortar, and centrifuged for 20 min at 1000 rpm and filtered. Filtrate was evaporated in oven up to dryness and dried extract was dissolved in 5 mL distilled water. 0.2-2.0 mL aliquot was taken in separate test tubes and volume was made up to 3 mL. Then 0.5 mL Folin-Ciocalteu reagent was added. After 3 min 2 mL of Na 2 CO 3 (20 %) was added and mixed. Test tubes were placed in boiling water bath for 1 min and then cooled. Optical density of the sample was recorded at 650 nm with the help of spectrophotometer (Spectronic 20D). The concentration was determined from the standard curve prepared using different concentrations of catechol (8-32 µg/mL) using the above procedure. The results were expressed as mg per 100 g on fresh weight basis and calculated as given below:

Degree of whiteness (Colour):-
The known weight of sample was macerated with distilled water and then filtered. The increase in absorbance of sample extract at 420 nm as per method was taken. Optical density of filtrate was measured by spectrophotometer (Spectronic 20D), using distilled water as a blank (Ranganna, 2010).

pH:-
The sample of mushroom was crushed with an equal quantity of distilled water and the pH was determined using digital pH meter after calibration with standard buffers of 4, 7 and 9 (Ranganna, 2010).

Visual observation:-
The colour and texture of the washed as well as stored mushroom were analyzed through sensory observation i.e. colour through visual observation whereas texture by the hand feel or sense of touch.

Statistical analysis:-
The data of the experimental observations during the above studies were computed for analysis of variance (ANOVA) using STATISTICA version 7 software of StatSoft Inc., Tulsa, Oklahoma, USA. The ANOVA was performed as per the completely randomized design (CRD). Experiment conducted in this study was replicated thrice.

Results and Discussion:-Weight loss:-
The data on weight loss is shown in Fig. 1 reveals that minimum weight loss was observed in mushrooms treated with 0.5 % KMS + 0.5 % NaCl + 0.5 % CaCl 2 solution which may probably be due to the CaCl 2 treatment as calcium helps in maintaining the cellular organization and regulating enzyme activities, thereby reducing moisture loss associated with senescence (Jones and Lunt, 1967). The loss in weight with increment in storage duration and temperature had also been reported by ( Among packaging materials, the maximum weight loss was observed in paper punnet with shrink wrapping (PPSW) followed by commercially used package (CU) and minimum in polypropylene (PP) irrespective of the washing treatment given to the mushroom. Mushroom stored at refrigerated condition had highest weight than the mushroom stored under ambient condition. This agreed with the findings of Burton and Noble (1993) who observed that weight loss from mushroom stored in open punnets at either 5° C (73 % RH) or 18° C (90 % RH) were linear, averaging 4 % per day at 5° C and 6 % per day at 18° C.

Moisture Content:-
A decrease in moisture content was noticed with the advancement of storage period in all the packaging materials irrespective of the storage conditions at which they were kept (Table 1). This could be attributed to the fact that 1793 mushrooms have a thin and porous epidermal structure, which is prone to quick superficial dehydration that causes significant quality losses (Singer, 1986). The maximum decrease in moisture content was recorded in T 1 i.e. plain water washing followed by T 2 (0.5 % KMS) and T 3 (0.5 % KMS + 0.5 % NaCl + 0.5 % CaCl 2 ). Mushroom packed with PPSW showed maximum reduction in moisture content when compared to other packaging materials, irrespective of the washing treatment given to them. The table clearly shows that the retention of moisture was best in mushrooms packed with PP after 3 days of storage at both temperatures. Antmann et al. (2008) reported that unpacked mushrooms show a weight loss of 72 % after 6 days of storage, suggesting that dehydration is a major factor for loss in mushroom quality during storage. The mushrooms stored at refrigerated conditions were better preserved than at ambient conditions, which was in accordance with Babitha and Kiranmayi (2010) who reported that tomatoes stored at refrigerated temperature had significantly higher moisture content than at ambient conditions at the first day of storage.
Total phenols:-Data on total phenol content of packed white button mushroom during storage are presented in Table 2. A significant decrease was recorded in the total phenol content with increase in the storage interval at both ambient and refrigerated conditions. The decrease in bioactivity of phenols may be attributed to their ability to chelate metals, inhibit lypoxgenase, and scavenge free radicals (Mallavadhani et al., 2006;Carmen and Xin, 2004). The maximum decrease in the total phenols was recorded in mushroom washed with plain water (T 1 ) when compared with mushroom washed with 0.5 % KMS (T 2 ) and 0.5 % KMS + 0.5 % NaCl + 0.5 % CaCl 2 (T 3 ). Among packaging materials, the phenolic content was observed to decrease less in mushroom packed in PP and maximum in PPSW. Altunkaya and Gokmen (2008) further reported that decrease in total phenol content may be probably due to the oxidation by polyphenol oxidase (PPO) during the storage of mushrooms.

Degree of whiteness (Colour):-
The amount of colour change depends upon the storage time and temperature. The copper containing enzymes tyrosinase, of the PPO group is largely responsible for the enzymatic discolouration of mushrooms (Nerya et al., 2006). The degree of browning in mushrooms increased rapidly during the time of storage (Fig. 2). The change in colour was more prominent in mushroom stored at ambient temperature as compared to mushroom stored at refrigerated temperature. The maximum browning was observed in mushroom with plain water washing and minimum in T 3 (0.5 % KMS + 0.5 % NaCl + 0.5 % CaCl 2 ). After 3 days of storage at refrigerated condition it was observed that mushrooms packed in PP has the lowest discolouration as compared to other packaging materials. The results were in agreement with results of Lopez-Briones et al. (1993) who reported that packaging of button mushroom in polypropylene film was beneficial in maintaining colour during storage for 8 days at 4°C.

pH:-
The increase in pH was observed in the mushrooms packed in different packaging materials at both ambient and refrigerated conditions as presented in Fig. 3. However, there was non-significant difference in the pH value when the effect of packaging materials on white button mushroom was taken into consideration during storage irrespective of the washing treatments. An increase in pH was recorded in mushroom treated with T 1 (plain water washing) followed by T 2 (0.5 % KMS) and T 3 (0.5 % KMS + 0.5 % NaCl + 0.5 % CaCl 2 ), irrespective of the packaging material used. Babarinde and Fabunmi (2009) also reported increase in pH of okra stored in polyethylene bag for 3 days, which implies that okra turn less acidic with increase in storage period.

Visual observation:-
A gradual decrease in firmness of packed mushrooms was observed with the advancement of storage period (Table 3 and 4) at both ambient and refrigerated conditions, which could be attributed to protein and polysaccharide degradation, hyphae shrinkage, central vacuole disruption and expansion of the intercellular space at the pileal surface (Zivanovic et al., 2000). Murr and Morris (1975) reported that change in texture is delayed due to a nonperforated film as the respiration rate decreases and development is retarded. Moreover, texture loss decreases when the CO 2 concentration increases (Lopez-Briones et al., 1992). Loss of water content in fresh mushroom has a direct relationship of phenol oxidase activity, which could be correlated with the visual degree of mushroom browning. The degradation of colour and texture was noticed in mushrooms after 3 days of storage at ambient condition, while the mushroom at refrigerated condition was acceptable up to 9 days of storage and then started to deteriorate, which was accompanied by the fungal growth. The maximum browning was observed in mushroom packed with PPSW and minimum with PP and those packed with LDPE, after 3 days of storage at both ambient and refrigerated conditions. At ambient condition, the slight yellowing of mushrooms was noticed in all the packaging materials 1794 accompanied by the formation of H 2 S gas inside the package. Among treatments, the mushroom treated with T 3 found to be best in retarding the degradation of colour and texture when compared to T 1 (plain water washing) and T 2 (0.5% KMS). Beelman and Simon (2000) reported that mushroom treated with 0.03 % CaCl 2 are more resistant to the adverse effects of excessive handling or bruising owing to vacuolar integrity improvement.