Application of Edible Oyster Mushroom, Pleurotus ostreatus...

INTRODUCTIONFood appearance is normally associated with color and is one of the primary attributes used by consumers to evaluate food quality. Factors such as naturally occurring pigments in foods and pigments due to both enzymatic and non-enzymatic reactions greatly influence the color of foods. Notably, enzymatic browning is one of the most well studied color reactions that affect fruits, vegetables, and seafood products. It is catalyzed by the enzyme polyphenoloxidase (PPO), generally used to

refer to tyrosinase (EC 1.14.18.1) and cathecoloxidase (EC 1.10.3.1) (José-Pablo et al. 2009). While enzymatic browning is essential to the overall acceptability of foods such as tea and cocoa, this can also bring devastating reactions in fruits, vegetables, and seafoods particularly in crustaceans. Severe blackspot formations or melanosis caused by enzymatic reaction in crustaceans can cause significant financial losses being a high value aquatic species (Kim et al. 2002). Such losses have prompted considerable interest in understanding and controlling PPO activity in foods, particularly in crustaceans. It was noted that in the diphenolase activity of PPO, both the oxy and met form reacts with o-diphenol with high catalytic

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Philippine Journal of Science147 (2): 231-238, June 2018ISSN 0031 - 7683Date Received: 01 Aug 2017

Key words: melanosis, mushroom extract, Penaeus vannamei, Pleurotus ostreatus, polyphenol oxidase, scavenging activity

Application of Edible Oyster Mushroom, Pleurotus ostreatus Extract to Control Postharvest Melanosis

in Shrimp, Penaeus vannamei

Marivic G. Llanto and Angel B. Encarnacion*

Department of Agriculture - Bureau of Fisheries and Aquatic Resources Region 02, Regional Government Center, Tuguegarao City, Cagayan 3500 Philippines

Control of the deteriorative effects of melanosis has been a challenge to the industry. Melanosis in crustaceans is normally controlled by means of direct application of various inhibitors such as 4-hexylresorcinol, sulfites, and phosphates. However, direct application of synthetic inhibitors to melanosis and antioxidants in food processing is usually restricted by considerations relevant to safety and effects on the food quality. This study attempted to apply a hot water extract prepared from the trimmings of edible oyster mushroom, Pleurotus ostreatus fruiting body to control melanosis in cultured Pacific white shrimp, Penaeus vannamei, through immersion technique. The antioxidative and antimelanosic properties of a hot water extract prepared from the trimmings of edible mushroom fruiting body were evaluated. The study compared the potential of the aqueous mushroom extract to prevent melanosis in cultured Pacific white shrimp with other antimelanosic compounds through immersion technique. The mushroom extract has high antioxidiative and antimelanosic activity. Immersion of marketable size shrimp in a 1.0% w/v solution of mushroom extract for 60 min significantly controlled melanosis in the treated shrimp during ice storage and comparable with the effects of 0.05% w/v ascorbic acid or sodium sulfite treatments. This study suggests that in vivo application of P. ostreatus extract through immersion technique can be an alternative to synthetic antimelanosic agents to inhibit postmortem melanosis in shrimp.

Corresponding author: [email protected], [email protected]

rate, oxidizing it to form o-quinone that leads to the production of a dark insoluble pigments called melanin. Notably, an increasing trend in the production of shrimp is again observed recently in the Philippines. Shrimp ranked third in the Philippine fisheries production with 51,5404 metric tons in 2016, contributing USD 36 million to the total export of the country (DA-BFAR 2016). Although Philippines farmed shrimp is still synonymous with black tiger shrimp, Penaeus monodon sharing the biggest chunk in the of total shrimp production, white shrimp, Penaeus vannamei and endeavor prawns production is also continuously increasing.

While there have been a lot of technologies and techniques developed to inhibit melanosis in food products such as crustaceans, new approaches are still under study. However, these alternatives must be evaluated in terms of its impact on the overall quality of food, effectiveness, cost, and regulatory status. It must be noted that due to health concerns, only a number of inhibitors are acceptable for food application based on government health regulations; thus, this research was conducted. The antioxidative and antimelanosic properties of a hot water extract prepared from the fruiting body of locally cultured edible mushroom, Pleurotus ostreatus was evaluated by immersion technique. P. ostreatus is known to contain significant amounts of antioxidants particularly 2-thiol-L-histidine-betaine (ergothioneine, ERT) (Dubost et. al 2007; Woldegiorgis et al. 2014; Bhattacharya et al. 2014). The production of this mushroom species has been noted to be increasing due to its demand in the locality; thus, a corresponding increase in waste during packaging and packing of mushroom, which are mostly edible trimmings. These edible trimmings from mushroom can be used for extraction and possible local and cheaper source of antioxidant and antimelanosic compound. The potential of the aqueous mushroom extract to prevent melanosis in shrimp was compared with other synthetic antimelanosic compounds being used by the food industry such as ascorbic acid and sodium sulfite in vivo through immersion technique. The extract, if found effective in preventing melanosis in shrimp, would greatly help the local industry in reducing postharvest losses.

MATERIALS

Raw Materials and Chemicals Trimmings of fresh oyster mushroom, Pleurotus ostreatus fruiting body were obtained from Angels Integrated Organic Products, Cataggamman Nuevo, Tuguegarao City, Cagayan. All chemicals used were analytical and technical grade and purchased from Sigma-Aldrich (St. Louis, MO).

Mushroom Extract Fresh oyster mushroom fruiting body trimmings were packed in plastic bags, delivered to the Integrated Fish Health and Fish Processing Laboratory of the Department of Agriculture - Bureau of Fisheries and Aquatic Resources, Regional Office No. 02, Tuguegarao City within an hour, and were processed immediately upon arrival. The mushroom extract was prepared following the procedure of Jang and co-authors (2002) with a slight modification. A 500 g portion of fresh mushroom fruiting body was mixed with 1000 mL of distilled water and boiled gently at 90°C for 30 min in a stainless steel pot. After cooling to room temperature, the mixture was initially filtered using cheesecloth and subsequently by qualitative filter paper No. 1. The filtrate obtained was evaporated at 50°C to obtain 500 mL of the hot water extract concentrate (1 g wet mushroom/mL of hot water extract). The extract was packed in sterile plastic tubes and stored at -20°C until used.

Determination of Radical Scavenging Activity2,2-Diphenyl-1-picrylhydrazyl (DPPH) radical scavenging activity of the mushroom extract (ME) was assayed following the method of Fu and co-authors (2002) with some modifications. An appropriate amount (0.02, 0.04 and 0.08 mL) of the buffer was replaced with the test solutions to determine their radical scavenging activities. The DPPH radical scavenging activity was calculated using the following formula:

DPPH scavenging activity (%) = (Acontrol – Asample/Acontrol) x 100 (1)

where Acontrol is the absorbance of the control mixture and Asample is the absorbance of the sample mixture containing the test solution. Analyses were done in triplicate.

Assay of PPO and its Inhibition by Mushroom Extract The inhibitory effects of ME on PPO activity were evaluated using an assay system consisting of 0.1 mL of 500 mM catechol, 0.1 mL of 500 mM L(-)-proline, 2.9 mL of 50 mM phosphate buffer (pH 6.8), and 0.1 mL of 100 units/mL PPO following the procedure of Jang and co-authors (2002) with a slight modification. An appropriate amount (0.02, 0.04, and 0.08 mL) of the buffer was replaced with the test solutions to determine their inhibitory activity on PPO. Absorbance at 530 nm (A530) was measured at 25°C after 5 min using a Shimadzu UV 1800 spectrophotometer. The following formula was used to calculate the inhibitory effects of the test solutions on PPO activity:

% inhibition = 100 – [(A × 100)/B] (2)

Philippine Journal of ScienceVol. 147 No. 2, June 2018

Llanto & Encarnacion: Mushroom Extract Controls Melanosis in Shrimp

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where A=A530 of the test sample and B=A530 of the control. Inhibition of PPO activity by 50% was determined using linear regression.

Experimental Organisms For this study, 200 individuals of marketable-size (15 g average weight) Pacific white shrimp P. vannamei harvested from the Northern Luzon Fisheries Technology Outreach Station, Sta. Teresita, Cagayan were used in the experiment. The newly harvested shrimps were transported with ice for one and a half hour to the Integrated Fish Health and Fish Processing Laboratory of the Department of Agriculture - Bureau of Fisheries and Aquatic Resources, Regional Office No. 02, Tuguegarao City and immediately used in the experiment upon arrival.

Dose Dependency Experiment To determine the dose dependency of the effect of the extract on melanosis prevention, four 6-L plastic container with 0.0%, 0.5%, or 1.0% (w/v) ME solution were prepared as part of the preliminary experiment. Three (3) groups of 20 shrimp were immersed in one of three (3) different solutions (0.0%, 0.5%, and 1.0%) for 60 min. After the immersion treatment, all shrimps were packed in plastic bags and then stored on ice for three (3) days. The shrimps were photographed with a digital camera and changes in the gray value of the carapace of cooked samples were evaluated using ImageJ software (2012 version, National Institute of Health, USA). Lower gray values denotes blackening or the development of melanosis in the carapace area of shrimp.

Immersion Time Dependency Experiment The 1% was the best concentration determined to effectively control melanosis in shrimp during ice storage for three (3) days. This concentration was used in the subsequent immersion time standardization experiment. Forty (40) pieces of Pacific white shrimp, P. vannamei were immersed in 1.0% ME solution at a ratio of 2:1 (v/w of shrimp) for 30 min and 60 min at 28°C. Rinsed shrimps without any treatment served as the control. After the immersion treatment, all shrimps were packed in plastic bags and then stored on ice for three (3) days. The shrimps were photographed with a digital camera and the gray values of the carapace of cooked samples were determined using ImageJ software. Lower gray values denotes blackening or the development of melanosis in the carapace area of shrimp.

Efficacy Comparison of Mushroom Extract to Other Antimelanosic Agents Having determined the best concentration and standardized the time of immersion to control melanosis in shrimp

during ice storage, the efficacy of the mushroom extract solution was then compared with a negative control (distilled water) and two positive controls: 0.05% (w/v) ascorbic acid (AA) and 0.05% (w/v) sodium sulfite (SS) solutions. Four groups of 20 shrimps each were immersed in one of four (4) different solutions (control, ME, AA, and SS). After the immersion treatment, all shrimps were packed in plastic bags, and then stored on ice for three (3) days. The shrimps were photographed with a digital camera and relative changes in the gray value of the carapace was evaluated using the following formula:

% relative change = 100 – [(A × 100)/B] (3)

where A is the actual gray value of the shrimp sample and B is the average gray value of the control samples. The gray value of the images was determined using ImageJ software. Lower gray values denotes blackening or the development of melanosis in the carapace area of shrimp.

Statistical Analyses Means and standard deviations (SD) for data were calculated using Microsoft Excel 2011. One-way analysis of variance was used to determine statistically significant differences between mean values. The level of significance was set at p<0.05.

RESULTS DPPH radical scavenging activity of the mushroom P. ostreatus hot water extract was determined (Figure 1). The effective amount of extract at which DPPH radical was scavenged by 50% was 0.056 mL in the assay system.

Figure 1. DPPH radical scavenging activity of the oyster mushroom, Pleurotus ostreatus extract. Results are presented as mean ± standard deviation (n=3). Values with different superscript letters represent significant difference (p<0.05) at the end of the reaction period.



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The DPPH radical scavenging activity of the extract was dose-dependent, suggesting that increasing the amount of the extract to the mixture significantly increase its radical scavenging activity.

Figure 2 shows the mushroom PPO inhibition activities of the mushroom hot water extract. With increasing amounts of extract, the mushroom PPO activity remarkably declined (p<0.05). At 0.08 mL of the mushroom extract in the assay system, 75% activity of the control was inhibited after 5 min. Polyphenoloxidase activity was inhibited by 50% at 0.039 mL of the mushroom extract in the assay system. Inhibition of PPO by the extract was

that treatment in 1.0% ME solution significantly inhibits the development of postharvest melanosis in shrimp.

Changes in color and the mean gray values of the carapace of the shrimps treated with mushroom extract at different immersion time are shown in Figures 5 and 6. By visual comparison (Figure 5), blackening of the carapace of the shrimp in the control group (0 min) was more intense than in the group immersed in the 1.0% mushroom extract for 30 min and 60 min as storage time progressed. Notably, Figure 6 shows that the mean gray values decreased

Figure 2. Inhibitory effects of oyster mushroom, Pleurotus ostreatus extract on the activity of mushroom polyphenoloxidase. Results are presented as mean ± standard deviation (n=3). Values with different superscript letters represent significant difference (p<0.05) at the end of the reaction period.

Figure 3. Changes in the mean gray values of carapace area of Pacific white shrimp, Penaeus vannamei during ice storage. Results are presented as the mean ± standard deviation (n=3). Values with different superscript letters represent significant difference between groups at different storage period (p<0.05).

Figure 4. Development of melanosis in the carapace area of Pacific white shrimp, Penaeus vannamei after three (3) days of ice storage.

also concentration dependent.

High DPPH radical scavenging activity and PPO activity inhibition of mushroom extract suggest that the extract has the potential to be an antioxidant and/or antimelanosic agent thus, the application to shrimps for the prevention of postharvest melanosis. Development of melanosis in shrimp samples during ice storage, as shown by changes in gray values on images of the carapace, is illustrated in Figure 3. After three (3) days of storage on ice, blackening in the carapace of the control group was more pronounced than in samples immersed in 0.5% and 1.0% ME solution. However, there is no significant difference between the control (0%) and 0.5% statistically thus, 1.0% ME solution was used in the succeeding experiment.

The result is supported by the aforementioned PPO activity inhibition of ME. With the increasing concentration of ME in the assay system, PPO activity is effectively inhibited. Visual inspection showed that immersion of shrimps in 1.0% ME solution effectively prevented the development of melanosis (Figure 4). These results show



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abruptly in the control samples after three (3) days of storage in ice compared to the other groups. However, the mean gray value of 30 min immersion was determined to be not significantly (p<0.05) different from the control group after three (3) days of ice storage thus, 60 min of immersion in 1.0% mushroom extract solution was used in the succeeding experiment.

Development of melanosis in shrimp samples during ice storage, as indicated by decreased mean gray values in images of the carapace, is shown in Figure 7. After two (2) days of storage on ice, blackening in the control group was more pronounced than in samples immersed in ME. Visual inspection shows that immersion in 1.0% ME effectively prevents the development of melanosis

(Figure 8). In addition, graphical analysis illustrates that mean gray values decreased more sharply on day 2 in the control group and 1.0% ME was similar to that of 0.05% AA and 0.05% SS. These results show that 1.0% ME inhibits the development of melanosis in shrimp.


Figure 6. Changes in the mean gray values of carapace area of Pacific white shrimp, Penaeus vannamei during ice storage. Results are presented as the mean ± standard deviation (n=3). Values with different superscript letters represent significant difference between groups at different storage period (p<0.05).


Figure 8. Development of melanosis and changes in the mean gray value of the carapace of Pacific white shrimp, Penaeus vannamei before and after ice storage. Results are presented as the mean ± standard deviation (n=3). Superscript letters above each data point represent statistically significant differences (p < 0.05).



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DISCUSSIONThe hot water extract from mushroom P. ostreatus fruiting body trimmings has an antioxidant potential as also reported initially by other researchers (Dubost et al. 2007; Woldegiorgis et al. 2014; Bhattacharya et al. 2014), suggesting that the extract contains active compounds responsible for its action. Notably, P. ostreatus contains an active antioxidant (ERT) ranging 1.35-3.78 mg/g dry weight based on the research of Woldegiorgis and co-authors (2014) and Bhattacharya and colleagues (2014). Such antioxidant was also found in edible mushroom Flammulina velutipes at 3.03 ± 0.07 mg/g, which also showed high radical scavenging activity against 2,2-diphenyl-1-picrylhydrazyl (DPPH), suppressed lipid oxidation in bigeye tuna meat, and stabilized fresh color of tuna meat during ice storage (Bao et al. 2008, 2009, 2010).

Basically, extracts that show high scavenging activity can inhibit PPO activities. Extract from the edible mushroom F. velutipes significantly inhibited PPO activity, prevented browning in apples, and delayed melanosis in shrimp during storage (Encarnacion et al. 2010, 2011a, 2011b, 2012a, 2012b; Jang et al. 2002, 2003). Furthermore, Encarnacion and co-authors (2010) found out that antioxidant ERT was also responsible for the antimelanosic property of the F. velutipes. In this study, the oyster mushroom fruiting body trimmings extract inhibited also mushroom PPO activity and melanosis in shrimp. This could have been due to the presence of antioxidant ERT in the extract.

Specifically, this study showed that immersing fresh shrimp in ME effectively inhibited postharvest melanosis in P. vannamei shrimp. Moreover, the development of melanosis in the carapace decreased as the concentration of the ME in the immersing solution increased and with longer immersion time. These effects may be due to greater absorption and accumulation of bioactive compounds such as ERT in the shrimp as the concentration of ME in the immersing solution increased and with longer immersion time. At 1.0% ME concentration, melanosis was effectively inhibited in shrimp samples after three days of ice storage and comparatively the same with the effect of 0.05% AA and better than 0.05% SS. Accumulation of extract in shrimp tissues may inhibit PPO activity in the carapace during postharvest. Like other studies on edible mushroom that contains bioactive compounds such as ERT, thiols like ERT are powerful nucleophiles that can chelate Zn2+ and Cu2+ (Hanlon 1971; Park et al. 2006; Encarnacion et al. 2012b) thus, melanosis in the shrimp immersed in the ME solution was inhibited.

In addition to having an inhibitory effect on PPO activity, mushroom extract from F. velutipes has been reported to suppress propolyphenol oxidase (proPO) gene expression

(Encarnacion et al. 2010, 2011a, 2011b, 2012a, 2012b). It has been known that PPO activation are carried out in a complex but carefully regulated series of events in the proPO activating system, that consists of proteins capable of binding to polysaccharides and other compounds associated typically with the microorganism and proteases that become active in the presence of microbial products (García-Carreño et al. 2008). Since immersing shrimp in mushroom extract significantly reduced hemolymph PPO activity in the study of Encarnacion and co-authors (2011a, 2011b, 2012a, 2012b), it is possible that the mushroom extract containing bioactive compounds such as ERT inhibited PPO activation. The observation of Encarnacion and co-authors (2010, 2011a, 2011b, 2012a, 2012b) that the expression of the proPO gene in hemocytes of mushroom-treated shrimp was lower than that in control shrimp supports this hypothesis. Thus, decreasing the expression of proPO reduces the amount that can be proteolytically activated into PPO (Adachi et al. 2003). Furthermore, in vitro experiments conducted by Encarnacion and co-authors (2010, 2011a, 2011b, 2012a, 2012b) showed that exogenous L-ERT and hexylresorcinol inhibitors also reduced proPO gene expression in haemocyte lysate supernatant (HLS). In particular, the PPO activity in L-ERT-treated HLS was very low.

The efficacy of ME in inhibiting postharvest melanosis is comparable to the efficacy of existing antimelanosic compounds such as AA and SS. The mechanism of AA in inhibiting postharvest melanosis is most likely due to its reducing power. The slight melanosis that occurred in AA-immersed shrimp after two (2) days of ice storage may be due to oxidation of AA that prevented it from reducing o-quinones, thereby allowing the formation of melanin (Guerrero-Beltran et al. 2005). Meanwhile, SS are known to inhibit both enzymatic and nonenzymatic browning reactions. Bisulfite was reported to inhibit melanosis by two mechanisms: by reacting with intermediate quinones in the melanosis reaction that forms sulfoquinones; and by irreversibly reacting with PPO, causing complete inactivation (Ferrer et al. 1989).

This study has shown that postharvest melanosis in P. vannamei shrimp can be effectively inhibited by immersing fresh sample in P. ostreatus mushroom extract. The efficacy of immersion in 1.0 % ME solution, in terms of melanosis inhibition was similar to that of both 0.05% AA and 0.05% SS solutions. Thus, P. ostreatus ME containing possible bioactive compounds particularly ERT is a promising natural alternative to the synthetic antimelanosic agents used to prevent postharvest melanosis in shrimps and other crustaceans.



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CONCLUSIONIn this study, the crude water extract from edible oyster mushroom fruiting body trimmings showed a remarkable scavenging activity against DPPH and inhibitory effect on PPO activity. Thus, the extract was used further to control melanosis in shrimp. Immersion of fresh shrimp, P. vannamei in a 1.0% crude extract of P. ostreatus mushroom extract for 60 min effectively inhibited postharvest melanosis. The efficacy of immersion in 1.0 % ME in inhibiting melanosis was similar to that of 0.05% AA and 0.05% SS. The biochemical interventions of edible oyster mushroom extract inhibited the PPO activity thus, melanosis was effectively controlled in treated P. vannamei shrimp samples comparable with the commercial antimelanosic agents. The extract could have contained active compounds particularly ERT that has been reportedly found in P. ostreatus and other mushrooms. The crude water extract from oyster mushroom fruiting body trimmings can be a cheaper, safer, locally available, and natural alternative to currently used synthetic antimelanosic compounds in the food industry. However, further improvements in the application may be considered in the future to shorten the immersion time while maximizing the use of the extract.

ACKNOWLEDGMENTSThe authors would like to thank Dr. Jovita P. Ayson, Dr. Milagros C. Morales, and staff of the DA-BFAR R02 for the support and assistance during the conduct of the study.

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