EFFECT OF SOME AMINO ACIDS ON YIELD AND CHARACTERISTICS OF PACIFIC WHITE SHRIMP TREATED WITH ALKALINE SOAKING SOLUTION

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1 PAPER EFFECT OF SOME AMINO ACIDS ON YIELD AND CHARACTERISTICS OF PACIFIC WHITE SHRIMP TREATED WITH ALKALINE SOAKING SOLUTION P. KINGWASCHARAPONG and S. BENJAKUL* Department of Food Tehnology, Faulty of Agro-Industry, Prine of Songkla University, Hat Yai, Songkhla 9112, Thailand *Corresponding author. Tel.: ; fax: address: ABSTRACT Effets of alkaline soaking solution (ASS),.75% NaOH ontaining 2.5% NaCl, ph 11.5, ontaining different amino aids at various onentrations on yield and harateristis of Paifi white shrimp (Litopenaeus vannamei) were studied. The lowest ooking loss with the highest ooking yield was otained for the sample treated with ASS ontaining 3% glutami aid (P<.5). When shrimp were treated with ASS having 3% monosodium glutamate (MSG) with the same mole equivalent to glutami aid, the higher weight gain ut slightly lower ooking yield were otained (P<.5). ASS ontaining 3% MSG had no effet on olor and shear fore of ooked shrimp. Keywords: glutami aid, monosodium glutamate, amino aids, alkaline, treatment, Paifi white shrimp Ital. J. Food Si., vol 28,

2 1. INTRODUCTION Nowadays, Paifi white shrimp (Litopenaeus vannamei) is one of important speies having a high market demand worldwide due to its appealed appearane, taste, flavor and texture (MANHEEM, 213). Thailand is well known as the world largest shrimp produer, manufaturer and exporter. In 213, shrimp was exported from Thailand with the value of 28,617 million ahts (THE CUSTOMS DEPARTMENT, 213). Shrimp proessing, espeially freezing, an lead to the denaturation or aggregation of proteins (CARNETRO et al., 213). These hanges an result in drip loss and sensorial hanges in the produt (GONÇALVES and RIBEIRO, 29). Furthermore, ooking also auses the hanges in quality attriutes, mainly y affeting textural and physiohemial properties and induing weight loss (CARNETRO et al., 213). The addition of water inding agent is therefore required in order to retain the quality of shrimp during proessing. Phosphate and iaronate have een widely used as water inding agents, whih an inrease water uptake and lower ooking loss (RATTANASATHERIN et al., 28; CARNETRO et al., 213 and CHATARASUWAN et al., 211). Biaronate treatment ould inrease the weight gain of shrimp, mainly due to the repulsion etween protein moleules mediated y its alkaline ph (CHATARASUWAN et al., 211). Due to the strit regulation of the uses of phosphate and iaronate in shrimp and shrimp produts, an alternative additive with the property equivalent to oth phosphate and iaronate are urrently gaining attention for shrimp proessing industry. Some amino aids were reported to retard protein denaturation and retain protein funtionality of frozen fish musle (CAMPO-DEANO et al., 29; ZHOU et al., 26). Owing to the hydrophili nature of some amino aids, their uses along with alkaline treatment ould show the synergism in water uptake or water inding of shrimp musle. Amino aid with different side hains, pi and moleular properties might exhiit varying effiay as proessing aid for shrimp proessing. Monosodium glutamate (MSG) is the sodium salt of glutami aid. It has een used widely as a flavor enhaner with umami taste. Sine it is readily solule in water, it an e used with ease for shrimp treatment and yield the produt with improved properties. However, no information regarding the uses of amino aids and their salts as the proessing aid for quality improvement of shrimp exists. The ojetive of this study was to investigate the impat of amino aids in onjuntion with alkaline treatment on yield and harateristis of Paifi white shrimp. 2. MATERIALS AND METHODS 2.1. Colletion and preparation of shrimp Paifi white shrimp (Litopenaeus vannamei) (55-6 shrimp/kg) were purhased from a loal market in Hat Yai, Songkhla provine, Thailand. Shrimp with storage time less than 6 h after apture were stored in the insulated ox ontaining ie using a shrimp/ie ratio of 1:2 (w/w). The samples were transported to the Department of Food Tehnology, Prine of Songkla University within 2 h. Upon arrival, shrimp were leaned using tap water. Shrimp were peeled and deveined manually. Prepared shrimp were plaed in polyethylene ag and stored in ie until use. Ital. J. Food Si., vol 28,

3 2.2 Effets of amino aids at various onentrations in alkaline soaking solution on weight gain, ooking loss and ooking yield of shrimp Preparation of treated shrimp Shrimp (peeled and deveined) samples were mixed with alkaline soaking solution (ASS;.75% NaOH ontaining 2.5% NaCl, ph 11.5) in the presene of glyine, glutami aid or arginine at levels of 1, 2 and 3% (w/v) using the shrimp/solution ratio of 1:2 (w/v). The mixtures were stirred gently for 3 min at 4 C and allowed to stand at 4 C for 3 min. After treatment, the shrimp samples were plaed on the plasti sreen for 5 min (4 C) to drain off solution. Sample soaked in 2.5% NaCl ontaining 3% mixed phosphates (sodium tripolyphosphate+tetrasodium pyrophosphate; 1:2, w/w) (MANHEEM, 213) and those treated with 2.5% NaCl ontaining.75% NaOH (ph 11.5) were used as the positive ontrols. Those without soaking were used as the ontrol. All shrimp samples without and with different treatments were divided into two portions. The first portion was used as raw shrimp and another portion was sujeted to ooking. To prepare ooked shrimp, the samples were sujeted to steaming until the ore temperature of the seond segment of shrimp reahed 85 C. The samples were ooled rapidly in ied water for 1 min, and drained on a sreen for 5 min at 4 C. Both raw and ooked shrimp samples were weighed and the weight gain, ooking yield and ooking loss were alulated Analyses Determination of weight gain Weight gain was determined y weighing the shrimps efore and after soaking in the solutions. Weight gain was alulated as follows: Weight gain (%) = [(B-A)/A] 1 where: A = initial weight (efore soaking) B = weight after soaking, followed y draining Determination of ooking loss and ooking yield Cooking loss and ooking yield were measured y weighing the shrimps efore and after heating aording to method of MANHEEM et al. (212). Cooking yield and ooking loss were alulated y the following equations: Cooking loss (%) = [(B-C)/B] 1 Cooking yield (%) = (C/A) 1 where: A = initial weight (without soaking and steaming) B = weight after soaking, followed y draining C = weight after steaming, followed y ooling in ied water Ital. J. Food Si., vol 28,

4 2.3 Effet of glutami aid at various onentrations in ASS adjusted to different phs on shrimp treatment Shrimp (peeled and deveined) samples were mixed with ASS (.75% NaOH ontaining 2.5% NaCl) in the presene of glutami aid at various onentrations (1, 2, and 3%) having ph 7 and To adjust the ph of ASS, 6 M and 2 M HCl was used. Shrimp samples were treated with solutions and analysed for weight gain, ooking loss and ooking yield as desried previously. 2.4 Comparative study of glutami aid and monosodium glutamate in ASS on shrimp treatment Preparation of treated shrimp Shrimp (peeled and deveined) samples were mixed with ASS (ph 11.5) in the presene of glutami aid or monosodium glutamate (MSG) at various onentrations (1, 2, and 3%) with ph of MSG was used at the same mole equivalent to glutami aid. Samples were treated as mentioned aove. Both raw and ooked shrimp were analysed for weight gain, ooking loss and ooking yield. Additional analyses were performed as follows: Determination of olor Color of raw and ooked shrimp were determined and expressed as L* (lightness), a* (greenness/ redness) and * (yellowness/ lueness). The seond segment of shrimp was sujeted for measurement using a Hunterla olorimeter (Hunter Assoiates Laoratory, In., Reston, Virginia, USA) using a CIE La sale (YOUNG and WHITTLE, 1985) Determination of shear fore Shear fore of raw and ooked shrimp was measured using the TA-XT2i texture analyzer (Stale Miro Systems, Surrey, England) equipped with a Warner-Bratzler shear apparatus (BRAUER et al., 23). The operating parameters onsisted of a ross head speed of 1 mm/s and a 25 kg load ell. The shear fore, perpendiular to the axis of the seond segment musle fiers, was measured Determination of protein pattern of soaking solutions After eing soaked with shrimp, the resulting soaking solutions were sujeted to SDS- PAGE to determine the patterns of proteins leahed out into solutions. SDS-PAGE was performed using 1% running and 4% staking gels as desried y LEAMMLI (197). Soaking solution (2 ml) was mixed with 1 ml of 1% (w/v) SDS solution. The mixture was then homogenized at 11, rpm for 1 min. The homogenate was inuated at 85 C for 1 h to dissolve total proteins. The sample was then entrifuged at 7,5 xg for 15 min to remove undissolved deris using a miroentrifuge (MIK-RO2), Hettih Zentrifugan, Tuttlingen, Germany). Protein onentration of the supernatant was determined y the Biuret method (ROBINSON and HOGDEN, 194). Sample (1 µg protein) was loaded onto the gel onsisting of 4% staking gel and 1% separating gel. Separation was performed y eletrophoresis apparatus (Mini-Protein III, Bio-Rad, USA) using 3 ma. Protein was fixed and stained for 3 h in 1.25% Coomassie Brilliant Blue R-25 in 4% methanol and 1% glaial aeti aid. Gels were destained for 15 min with destaining Ital. J. Food Si., vol 28,

5 solution I (5% methanol and 7.5% glaial aeti aid) and with the destaining solution II (5% methanol and 7.5% graial aeti aid) for 3 h. Wide range moleular weight standards were used and the moleular weight of protein was estimated Sensory evaluation Cooked samples were sujeted to sensory analysis. The samples were evaluated y 3 panelists from the Department of Food Tehnology with the age of 25-35, using the 9-point hedoni sale, where 9 = like extremely; 7= like moderately; 5 = neither like or not dislike; 3 = dislike moderately; 1 = dislike extremely (MEILGAARD et al., 199). Panelists were aquainted with shrimp onsumption and had no allergies to shrimp. All panelists were asked to evaluate for olor, appearane, flavor, taste, texture and overall likeness. Samples were presented in the plates oded with three-digit random numers Statistial analyses A ompletely randomized design (CRD) was used for the whole experiments. Experiments were run in tripliate using different lots of shrimp samples. Data were sujeted to analysis of variane and mean omparison was arried out using Dunan s multiple range test. Statistial analyses were performed using the Statistial Pakage for Soial Siene (SPSS 11. for window, SPSS In., Chiago, IL, USA). 3. RESULTS AND DISCUSSION 3.1 Weight gain, ooking loss and ooking yield of Paifi white shrimp treated with ASS ontaining amino aids at various onentrations Weight gain of Paifi white shrimp treated with ASS (ph 11.5) in the presene of amino aids at different onentrations (1, 2 and 3%) is shown in Fig. 1a. Weight gain of the treated shrimp inreased, when the onentrations of amino aids in ASS inreased (P<.5), exept those treated with ASS ontaining glutami aid, in whih weight gain dereased with inreasing onentration (P<.5). Amongst all amino aids, glutami aid showed the higher inreasing effet on weight gain at low level (1%). Under the alkaline ondition, aroxyl groups, oth at α-aron and γ-aron, were deprotonated and COO eame dominant. Those negatively harged residues might penetrate into the swollen musle along with ASS. Some COO groups of glutami aid ould interat with positively harged domain of proteins via ioni interation, while the rest of COO groups were ale to ind with water. As a result, the water ould e retained in the musle after treatment. Nevertheless, in the presene of an exessive glutami aid, those COO groups in the solution (aqueous phase) more likely ompeted with musle proteins in inding with water. As a onsequene, the less water was retained in the shrimp musle as indiated y the lowered weight gain, when the level of glutami aid in ASS was higher than 1%. Glyine has een known as the smallest amino aid and has H atom as the side hain. Due to its small moleule, it ould migrate easily into shrimp musle and susequently interat with water y hydrogen onding via side hains within musle. Additionally, aroxyl groups at α-aron of glyine, whih was deprotonated under the alkaline ondition, ould interat with water via ioni interation. Consequently, water ould e more imied, partiularly when the level of glyine inreased. This was refleted y the inreased weight gain of shrimp after eing treated with glyine at higher onentrations. Ital. J. Food Si., vol 28,

6 For shrimp treated with ASS ontaining arginine, weight gain inreased as the levels of arginine inreased (P<.5). At ph 11.5, some aroxyl groups of arginine (pi=1.76) eame deprotonated. Those groups ould interat with musle proteins and simultaneously ound with water. It was noteworthy that ph of solution (11.5) was lose to pi of arginine. Therefore, COO group of arginine in ASS was present at low intensity. Owing to the lower aundane of COO group in ASS ontaining arginine, water was less ound with proteins, in omparison with that ontaining glutami aid. WOLFENDEN et al. (1981) found that hydration potential of arginine was high at ph 7. At neutral ph, NH 2 + group mostly eame protonated, in whih NH 3 was formed. Those positively harged groups effetively ound with water. However, in the present study, the ph of solution + was 11.5, whih was aove pi (1.76). As a result, NH 3 was not present in ASS, and NH2 group at the side hain eame aundant. Arginine is also reported frequently to form hydrogen onds with other side hains and water moleule (BORDERS et al., 1994). Thus, harge of amino aid under the alkaline ondition and the way those amino aids interated with water and proteins in musle more likely affeted weight gain of treated shrimp. Differenes in weight gain among all treatments were plausily governed y the differenes in water inding or water holding apaity of different amino aids under the alkaline onditions. It was found that weight gain of shrimp treated with ASS ontaining 3% arginine was higher than those treated with mixed phosphates and other samples (P<.5). It is noted that treatment of shrimp with ASS ontaining 1% glyine, 1% arginine or 3% glutami aid led to the lower weight gain, ompared with ASS without amino aids. Thus, amino aids in alkaline solution had varying impat on weight gain of shrimp after treatments. Cooking loss and ooking yield of shrimp samples treated with ASS ontaining different amino aids at various onentrations are shown in Figs. 1 and 1, respetively. Cooking loss of shrimp dereased when the onentration of glutami aid in ASS inreased (P<.5). However, no differenes in ooking yield were notieale, when glyine at different levels was used (P>.5). Overall, when shrimp samples were treated with ASS in the presene of all amino aids, the derease in ooking loss was otained, in omparison with those treated with only ASS (P<.5). The weight loss was in the desending order in samples treated with ASS ontaining glyine, arginine and glutami aid, respetively. Shrimp treated using ASS omprising 3% glutami aid had the lower ooking loss than that treated with M-P (P<.5). Generally, the lowest ooking loss was found with the sample treated with ASS ontaining 3% glutami aid (P<.5). When heat was applied, denaturation and oagulation of proteins were augmented, whih in turn lowered water-holding apaity. Moreover, the inreased protein-protein interation was otained (NIAMNUY et al., 28), leading to the enhaned release of water from shrimp musle. After ooking, the ooking yield of shrimp with different treatments varied (Fig. 1), in whih water moleules might e ound with amino aids or proteins in different fashions. The highest ooking yield was otained with shrimp treated with ASS ontaining glutami aid, ompared with other treatments (P<.5). It was suggested that glutami aid had the potential to ind water in shrimp musle, when heat was applied. The effiay in water holding during heating was dependent on onentrations used (P<.5). However, the onentration of glyine had no effet on ooking yield of shrimp (P>.5). Effiieny in inreasing ooking yield was in the desending order: glutami aid, arginine and glyine. The negatively harged residues, espeially aroxyl group at α-aron and γ-aron of glutami aid are strongly hydrated (COLLINS et al., 27). The two amino aids that have the highest water-inding aility are asparti aid and glutami aid (LOW et al., 1978). An Ital. J. Food Si., vol 28,

7 ioni side hain of asparti aid, glutami aid and lysine has een laimed to ind 4-7 water moleules (ZAYAS, 1997). Weight gain (%) e d d d d a a d f (a) Cooking loss (%) h g f f f a d de e () Cooking yield (%) a g f g h () d e f Figure 1: Weight gain (a), ooking loss () and ooking yield () of Paifi white shrimp treated with.75% NaOH ontaining 2.5% NaCl (ph 11.5) in the presene of amino aids at different onentrations. Note: M-P: solution ontaining 2.5% NaCl and 3% mixed phosphates (tetrasodium pyrophosphate and sodium tripolyphosphate, 2:1, (w/w)), ASS:.75% NaOH ontaining 2.5% NaCl (ph 11.5), Gly: glyine Glu: glutami aid, Arg: arginine. Different lowerase letters on the ars indiate signifiant differenes (P<.5). Bars represent the standard deviation (n=3). Ital. J. Food Si., vol 28,

8 When omparing with the sample treated with ASS alone, all samples treated with amino aids showed the inreased ooking yield (P<.5). Only sample treated with ASS ontaining 3% glutami aid had the higher ooking yield than that treated with M-P (P<.5). The sample treated with ASS having 2% glutami aid had similar ooking yield to those treated with mixed phosphate (P>.5). Therefore, glutami aid in ASS was shown to play a vital role in inreasing the ooking yield y holding water in musle during heating. 3.2 Weight gain, ooking loss, ooking yield and physial properties of Paifi white shrimp treated with ASS ontaining glutami aid at various onentrations and phs Weight gain, ooking loss and ooking yield of Paifi white shrimp samples after soaking in ASS in the presene of glutami aid at various onentrations with different phs (7. and 11.5) are shown in Fig. 2. Weight gain and ooking yield of shrimp samples soaked in ASS, ph 11.5 were higher than those treated with ASS at ph 7. (P<.5), for all onentrations of glutami aid used. At ph aove pi or very alkaline ph, proteins had more negative harge, in whih protein moleules repulsed eah other, resulting in the swollen musle struture (CHANTARASUWAN et al., 211). As a onsequene, water ould e more uptaken into shrimp (CHANTARASUWAN et al., 211). Simultaneously, glutami aid ould e taken into the musle along with NaCl. Glutami aid might favor the water inding via its COO - group. Weight gain was slightly dereased as the onentrations of glutami aid used inreased (P<.5), regardless of ph. Generally, weight gain of all samples was lower than that of samples treated with ASS and with M-P (P<.5), exept that treated with ASS ontaining 1% glutami aid (ph 11.5) that showed the similar weight gain (P>.5). Among Paifi white shrimp treated with sodium aronate and sodium iaronate at various phs ( ), the highest weight gain and ooking yield were oserved in those treated at ph 11.5 (CHANTARASUWAN et al., 211). Therefore, ph of soaking solution was the prime fator determining weight gain of shrimp. Cooking loss (Fig. 2) of shrimp dereased, when the onentration of glutami aid in ASS inreased (P<.5), irrespetive of ph used. Lower ooking loss was found as ASS had ph of 11.5, ompared with ph 7. (P<.5). The derease in ooking loss was in aordane with the inrease in ooking yield. The lowest ooking loss was oserved in shrimp soaked with ASS ontaining 3% glutami aid (ph 11.5) (P<.5). Glutami aid ould provide negative harge to musle, therey enhaning the water inding apaity of musle proteins. Bound water was held tightly during heating as indiated y the lowered ooking loss and inreased ooking yield. AASLYNG et al. (23) suggested that a higher ooking loss was found in the sample with the low ph, whereas high water holding apaity was ahieved at medium and high ph. When omparing the ooking loss of shrimp treated with mixed phosphates (M-P), the sample treated with ASS ontaining glutami aid at levels of 2 or 3% (ph 11.5) had the lower ooking loss (P<.5). This refleted the high effiieny of ASS ontaining glutami aid at a suffiient amount in lowering the ooking loss. The augmented repulsion of musle ompartment also allowed glutami aid with the high negative harge to penetrate into musle and ind more water, thus resulting in the lowered ooking loss. In the presene of glutami aid at 2 and 3%, no differenes in ooking yield were otained, ompared with the sample treated with ASS alone (P<.5), when ph of soaking solution was 7. (Fig. 2). On the other hand, ooking yield of samples treated with ASS ontaining glutami aid at all levels were higher than that of sample treated with ASS alone, when ph was 11.5 (P<.5). The result indiated the paramount role of ph in water holding apaity of musle when heating was implemented. As the shrimp were treated Ital. J. Food Si., vol 28,

9 with ASS (ph 11.5) ontaining glutami aid at levels higher than 1%, similar ooking yield was otained, ompared to that found in the sample treated with mixed phosphates (P<.5). Therefore, ASS ontaining glutami aid showed the potential in improving the ooking yield, and its effiay was omparale to mixed phosphates Weight gain (%) f e a de d (a) ph 7 ph 11.5 Cooking loss (%) g f f e d a () ph 7 ph 11.5 Cooking yield (%) a e d de f () ph 7 ph 11.5 Figure 2: Weight gain (a), ooking loss () and ooking yield () of Paifi white shrimp treated with.75% NaOH ontaining 2.5% NaCl with phs 7. and 11.5 in the presene of glutami aid at various onentrations. Note: M-P: solution ontaining 2.5% NaCl and 3% mixed phosphates (tetrasodium pyrophosphate and sodium tripolyphosphate, 2:1, (w/w)), ASS:.75% NaOH ontaining 2.5% NaCl (ph 11.5), Glu: glutami aid. Different lowerase letters on the ars indiate signifiant differenes (P<.5). Bars represent the standard deviation (n=3). Ital. J. Food Si., vol 28,

10 3.3 Comparative study of ASS ontaining glutami aid and MSG on shrimp treatment Glutami aid with high effiay in inreasing ooking yield was seleted as the potential additive in ASS. However, glutami aid had low soluility. Conversely, MSG, a salt form, was heaper and solule with ease in water. MSG was used at the same mole equivalent to glutami aid for shrimp treatment Weight gain, ooking loss and ooking yield Weight gain of shrimp treated with ASS ontaining glutami aid at the levels of 1%, 2% and 3% or MSG at the levels of 1%, 2% and 3% mole equivalent of glutami aid is shown in Fig. 3a. Sample treated with ASS ontaining 1 or 2% MSG had similar weight gain to that treated with mixed phosphate (positive ontrol) (P>.5). It was postulated that the negatively harged glutami aids from MSG were ale to ind tightly with water moleule via ioni interation within protein ompartment, leading to the inreased water holding in shrimp musle. It was found that MSG showed higher aility in water holding than glutami aid as indiated y higher weight gain. For ooking loss (Fig. 3), shrimp treated with ASS ontaining MSG had the higher ooking loss than those treated with glutami aid ounterpart, partiularly at levels of 2 and 3% (P<.5). The ooking loss was lower in samples treated with ASS omprising oth glutami aid and MSG at higher onentrations (P<.5). For samples treated with mixed phosphate and ASS alone, the ooking losses of 19.19% and 31.7%, respetively were oserved. The ooking loss of % was otained for sample treated with ASS having glutami aid, while ooking loss of % was found for the sample treated with ASS ontaining MSG. During ooking, musle proteins underwent denaturation to a higher extent, while the amount of water retained in shrimp meat dereased with oinidental inrease in fat and protein ontents (MANHEEM et al., 212; BENJAKUL et al., 28). The result suggested that shrimp musle ould retain more water when glutami aid and MSG were inorporated in ASS. However, glutami aid showed the slightly higher aility in lowering ooking loss of shrimp, ompared with MSG, espeially at level of 2-3%. For ooking yield (Fig. 3), the opposite results were oserved, in omparison with ooking loss. The lowest ooking yield was oserved in the ontrol (without treatment). Cooking yield of treated shrimp inreased, when the onentrations of oth glutami aid and MSG inreased (P<.5). Similar ooking yield was found in shrimp treated with ASS ontaining 2% glutami aid or 3% MSG (P>.5). It was found that shrimp treated with ASS ontaining 2 or 3% glutami aid or 3% MSG had the higher ooking yield than that of sample treated with mixed phosphates (P<.5). Sine MSG was more solule and heaper than glutami aid, it was seleted for treatment of shrimp. The appropriate onentration of MSG in ASS was 3% Shear fore Shear fore of raw and ooked Paifi white shrimp treated with ASS (ph 11.5) in the presene of glutami aid and MSG at different levels (1%, 2% and 3%) is presented in Tale 1. For raw shrimp, all treatments had no impat on shear fore (P>.5). It was noted that shrimp treated with ASS ontaining glutami aid and MSG at all levels (1-3%) had similar shear fore (P>.5). All samples treated with ASS ontaining either glutami aid or MSG had the similar shear fore to those treated with mixed phosphates (P>.5), exept those treated with ASS ontaining 3% glutami aid, whih showed the lower shear fore (P<.5). Generally, shrimp tended to have the non-signifiant derease in shear Ital. J. Food Si., vol 28,

11 fore after treatment, partiularly with inreasing onentrations of glutami aid and MSG in ASS used for treatment. When proteins imied water within their struture, the musle had the lower resistane to the fore applied. Weight gain (%) e e d (a) a Cooking loss (%) f e d d a () Cooking yield (%) a d d e f d e () Figure 3: Weight gain (a), ooking loss () and ooking yield () of Paifi white shrimp treated with.75% NaOH ontaining 2.5% NaCl (ph 11.5) in the presene of glutami aid and MSG at various onentrations. Note: M-P: solution ontaining 2.5% NaCl and 3% mixed phosphates (tetrasodium pyrophosphate and sodium tripolyphosphate, 2:1, (w/w)), ASS:.75% NaOH ontaining 2.5% NaCl (ph 11.5), Glu: glutami aid. MSG: monosodium glutamate. Different lowerase letters on the ars indiate signifiant differenes (P<.5). Bars represent the standard deviation (n=3). Ital. J. Food Si., vol 28,

12 Tale 1: Shear fore of raw and ooked of Paifi white shrimp treated with.75% NaOH (ph 11.5) ontaining 2.5% NaCl in the presene of glutami aid and MSG at various onentrations. Treatments Shear fore (g) Raw Cooked No treatment 197±177,a 2194±326 M-P 257± ±341 a ASS 189±416 a 231±345 ASS+1% MSG 2127± ±13 a ASS+2% MSG 1995±284 a 1525±334 a ASS+3% MSG 1794±275 a 1472±83 a ASS+1% glu 1972±329 a 1555±25 a ASS+2% glu 1665±253 a 1515±126 a ASS+3% glu 1618±243 a 1449±118 a Mean±SD (n=3). Note: M-P: solution ontaining 2.5% NaCl and 3% mixed phosphates (tetrasodium pyrophosphate and sodium tripolyphosphate, 2:1, (w/w)), ASS:.75% NaOH ontaining 2.5% NaCl (ph 11.5), Glu: glutami aid. MSG: monosodium glutamate. Different lowerase supersripts in the same olumn indiate signifiant differenes (P<.5). For ooked shrimp, lower shear fore was oserved in all treated samples, in omparison with those without treatment and those treated with ASS alone (P<.5). Nevertheless, all samples had the similar shear fore, ompared to those treated with mixed phosphates (P>.5). When heat was applied, protein denaturation and aggregation took plae. Those phenomena resulted in the toughness as well as high resistane to fore. No differenes in shear fore were found among shrimp treated with ASS ontaining glutami aid and MSG at different onentrations used (P>.5). Myofirillar proteins with inreased negative harge favored the repulsion of polypeptide hains, whih resulted in the swelling of musle and eame less resistant to shear fore applied. When the onentration of glutami aid or MSG in ASS inreased, non-signifiant derease in shear fore was otained (P>.5). Therefore, treatment of shrimp using ASS ontaining glutami aid or MSG did not had the negative impat on textural property and their shear fore was omparale to that of shrimp treated with mixed phosphates Color Color parameters (L*, a* and *) of raw and ooked shrimp treated with ASS (ph 11.5) in the presene of glutami aid or MSG at different onentrations are shown in Tale 2. For raw shrimp, L* value inreased when onentrations of MSG in ASS inreased (3%) (P<.5). The a* value generally inreased as the onentrations of oth glutami aid and MSG in ASS inreased (P<.5). Basially, a* value indiates the reddish olor. Conversely, no hanges in * value were oserved as the level of glutami aid or MSG in ASS inreased (P<.5). Thus, raw shrimp turned to e slightly reddish as the levels of glutami aid or MSG in ASS inreased. Appearane of the produt plays a signifiant role in maintaining high onsumer aeptane (BONO et al., 212). Glutami aid or MSG in ASS might indue the hange of proteins assoiated with arotenoid, named arotenoprotein. This led to the enhaned exposure of free arotenoids, espeially astaxanthin, as evidened y more reddish olor. Astaxanthin was reported as the major Ital. J. Food Si., vol 28,

13 pigment in shrimp meat (NIAMNUY et al. 28). After ooking, no differene in olor was oserved among shrimp treated with ASS ontaining glutami aid or MSG at all levels (P>.5). It was ovious that L*, a* and *-values of ooked shrimp inreased, in omparison with raw ounterparts. The inrease in intensity of red olor alter ooking is aused y musle protein denaturation and the release of arotenoid pigment ound to the protein (arotenoproteins) (LATSCHA 1989; NIAMNUY et al. 28). The a*- and *- values of samples treated with ASS ontaining 2 or 3% glutami aid were lower, ompared with the ontrol (no treatment). During soaking, some proteins inluding arotenoproteins were partially soluilized or leahed out. As the results, less pigments were retained in the meat. Coinidentally, the soaking solution was more reddish in olor as the glutami aid or MSG onentrations in ASS inreased (data not shown). There was no differene in all olor parameters etween ooked shrimp treated with ASS ontaining glutami aid or MSG at all levels and those treated with mixed phosphates. Tale 2: Color of raw and ooked of Paifi white shrimp treated with.75% NaOH (ph 11.5) ontaining 2.5% NaCl in the presene of glutami aid and MSG at various onentrations. Samples Treatments L* a* * Raw No treatment 46.46±1.58 a -1.64±1.5 a.12±1.91 d M-P 46.33±3.43 a -1.69±.36 a -3.23±1.79 a ASS 44.96±2.1 a -1.66±.34 a -2.1±1.61 a ASS+1% MSG 45.42±2.58 a.27± ±.48 ASS+2% MSG 46.81±2.1 a 1.28± ±1.28 ASS+3% MSG 48.87± ±1.15 d.16±1.96 d ASS+1% glu 45.22±2.39 a.89± ±1.63 d ASS+2% glu 46.9±.88 a 2.1±.74 d.8±1.95 d ASS+3% glu 46.35±1.22 a 2.77±.87 d 1.19±2.71 d Cooked No treatment 7.2± ±4.4 d 16.34±3.98 M-P 65.5±4.3 a 8.55±2.45 a 12.37±4.63 a ASS 69.35± ±4.2 d 13.39±3.2 a ASS+1% MSG 65.9±2.4 a 11.17±2.77 ad 14.34±3.86 a ASS+2% MSG 64.77±3.95 a 8.86±1.31 a 11.28±3.63 a ASS+3% MSG 63.17±4.55 a 8.27±1.94 a 1.92±3.18 a ASS+1% glu 65.5±3.75 a 11.32±1.91 d 15.64±3.6 a ASS+2% glu 64.94±2.38 a 9.69±1.6 a 14.4±3.13 a ASS+3% glu 64.44±2.5 a 9.4±1.3 a 11.78±2.18 a Mean±SD (n=3). Note: M-P: solution ontaining 2.5% NaCl and 3% mixed phosphates (tetrasodium pyrophosphate and sodium tripolyphosphate, 2:1, (w/w)), ASS:.75% NaOH ontaining 2.5% NaCl (ph 11.5), Glu: glutami aid. MSG: monosodium glutamate. Different lowerase supersripts in the same olumn under the same state of sample indiate signifiant differenes (P<.5) Protein patterns of soaking solutions Protein patterns of soaking solutions after shrimp treatments are shown in Fig. 4. Band intensity of myosin heavy hain (MHC) and atin slightly inreased as onentration of oth glutami aid and MSG in ASS inreased. The result suggested that more MHC and atin were soluilized and leahed out to solution to a higher extent when glutami aid and MSG levels in ASS inreased. The inrease in MHC and intensity in soaking Ital. J. Food Si., vol 28,

14 solutions was in agreement with the higher ooking yields (Fig. 3). Protein extration and dissoiation of myofirillar proteins were mainly due to the ioni effet and ph alteration (BENDALL, 1954). Apart from MHC and atin, protein with MW of 25.6 and 18.2 kda also inreased with inreasing levels of glutami aid and MSG in ASS. CHANTARASUWAN et al. (211) reported that Paifi white shrimp soaked in sodium iaronate and sodium aronate solution had the inrease in and intensity of MHC as ph of soaking solution inreased. Protein patterns of ASS and ASS with mixed phosphates after shrimp soaking were similar, in whih atin and protein with MW of 18.2 kda were dominant. After those proteins were leahed out from shrimp musle, the soaking solution ould e more penetrated to looser musle ompartment and retained inside the musle as indiated y higher weight gain and ooking yield. k Da MHC Atin kda 18.2 kda 12.6 kda M M A 1 -P SS ASS ASS+MS Figure 4: Protein patterns of soaking solution (.75% NaOH and 2.5% NaCl, ph 11.5) in the presene of glutami aid and MSG solutions at different onentrations after soaking with shrimp. M, Standard marker; M-P: solution ontaining 2.5% NaCl and 3% mixed phosphates (tetrasodium pyrophosphate and sodium tripolyphosphate, 2:1 (w/w)), ASS:.75% NaOH ontaining 2.5% NaCl (ph 11.5), MSG: monosodium glutamate, MHC: myosin heavy hain. Numers indiate the onentration of Glu or MSG (%). 3.4 Sensory properties of ooked shrimp treated with alkaline soaking solution ontaining MSG Sensory properties of ooked shrimp without and with different treatments are shown in Tale 3. The lowest likeness sore for all attriutes tested exept flavor was found in the ontrol sample (without treatment) (P<.5). During heating, the shrinkage of musle of shrimp ourred, resulting in more ompat in mirostruture of shrimp with less juiiness. Among all samples, ASS +3%MSG sample showed the highest sore for all attriutes exept for flavor that showed the lower sore than the ontrol and M-P sample Ital. J. Food Si., vol 28,

15 (P<.5). This might e assoiated with fishy odor/flavor developed in of ASS +3%MSG sample. MSG is sodium salt of glutami aid and provides a flavoring funtion similar to naturally ourring free glutamate in foods (YAMAGUCHI and NINOMIYA, 2). Monosodium L-glutamate (MSG) has een used as a flavor enhaner sine 198, when it was identified as the soure of umami taste (pleasant savory taste) (IMADA et al., 214). Sine ASS +3%MSG samples had the high water holding apaity, more water was retained in shrimp meat as shown y a high ooking yield (Fig. 3). Dereased toughness with high juiiness ontriuted to the higher likeness sore for texture and appearane. For olor likeness, the highest sore was oserved for ASS +3%MSG sample (P<.5). Treatment of shrimp using.75% NaOH ontaining 2.5% NaCl and 3% MSG (ASS+3%MSG) rendered the resulting ooked shrimp with the highest overall likeness sore (P<.5). However, the sore was similar to that of shrimp treated with mixed phosphates (P>.5). Tale 3: Likeness sore of ooked Paifi white shrimp with different treatments. Attriutes No treatment M-P ASS ASS+3% MSG Appearane 5.5±1.25,a 7.76±.66 7.±.98 8.±.74 Color 6.3±1.56 a 7.76± ± ±.82 Flavor 7.1± ± ±1.19 a 6.4±1.57 a Texture 5.57±2.1 a 7.55±.81 7.± ±.85 Taste 5.8±1.85 a 7.83± ± ±.73 Overall 5.77±1.45 a 7.76± ± ±.69 Mean±SD (n=3). Note: M-P: solution ontaining 2.5% NaCl and 3% mixed phosphates (tetrasodium pyrophosphate and sodium tripolyphosphate, 2:1 (w/w)), ASS:.75% NaOH ontaining 2.5% NaCl (ph 11.5), ASS+3% MSG:.75% NaOH ontaining 2.5% NaCl (ph 11.5) in the presene of 3% monosodium glutamate. Different lowerase supersripts in the same row indiate signifiant differenes (P<.5). 4. CONCLUSION Amino aids in ASS had the pronouned impat on quality improvement of Paifi white shrimp. Glutami aid showed the marked effet on inreasing ooking yield, while arginine ould inrease weight gain effetively. ph of ASS played a paramount role in water uptake and lowering the ooking loss of treated shrimp. MSG, the water solule salt, showed the omparale impat on quality improvement to glutami aid. Glutami aid or MSG at higher level in ASS enhaned the soluility of MHC and atin, failitating the migration of soaking solution and water holding apaity of shrimp musle. Cooked shrimp treated with ASS ontaining MSG had the inreased overall likeness sore, ut showed less sore in flavor assoiated with the slightly fishy odor. The use of ASS ontaining 3% MSG was reommended as the promising soaking solution for shrimp treatment. ACKNOWLEDGEMENT This work was supported y National Researh Counil of Thailand and Prine of Songkla University, Thailand. The TRF Distinguished Researh Professor Grant was also aknowledged for the finanial support. Ital. J. Food Si., vol 28,

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