Extractive Component Changes in the Foot Muscle of Live Small Abalone During Storage

FISHERIES SCIENCE 2002; 68: 380–387

Original Article

Extractive component changes in the foot muscle of live small abalone during storage

Tze-Kuei CHIOU,1* Meng-Mei LAI,1 Huei-Ling LAN2 AND Chyuan-Yuan SHIAU1

1Department of Food Science, National Taiwan Ocean University, and 2Department of Fisheries Technology, Taiwan Fisheries Research Institute, Keelung, Taiwan 202

ABSTRACT: Changes in the freshness indices and extractive components in the foot muscle of live small abalone Haliotis diversicolor during storage at 5∞C, 15∞C, and 25∞C were investigated. The pH values declined with storage time. Volatile basic nitrogen and the K-value increased gradually with storage time at 15∞C and 25∞C, but changes were small at 5∞C. The onset of initial decomposition of samples was observed after 3.5 days at 5∞C, after 2.5 days at 15∞C, and after one day at 25∞C. Adenosine triphosphate and adenosine diphosphate degraded rapidly within the early days of storage. In contrast, levels of adenosine monophosphate increased and exhibited prolonged accumulation throughout the storage period. The total amount of free amino acids increased markedly during storage. The dominant free amino acids, such as taurine, glutamic acid, glycine, alanine, and arginine, also increased after storage.

KEY WORDS: extractive component, freshness index, small abalone, storage.

INTRODUCTION Sawyer et al. have examined the sensory properties of fish and concluded that flavor is the Abalone is a highly valued delicacy with a unique most important factor determining consumer taste and texture.1,2 According to a previous study acceptance, whereas texture is of greater relative we conducted,3 the composition of extractive com- importance for those who dislike fish.13 The con- ponents in the small abalone muscle is similar to tributions by extractive components to the sensory that of Japanese abalone.4–7 Regarding the con- attributes and taste specificity of seafoods have sumption of seafoods, the changes in the extractive been reviewed.14,15 Based on such sensory test components in fish and shellfish during storage results, glutamic acid (Glu), glycine (Gly), alanine have been investigated extensively in relation to (Ala), arginine (Arg), taurine (Tau), and adenosine the assessment of freshness and flavor qualities, monophosphate (AMP) are considered the taste- and to understand the features of postmortem bio- active components in shellfish such as snow crab,16 chemical changes; however, few studies on live scallop,17 and short-necked clam;18 whereas Glu, shellfish have been done.8 Although there have Gly, AMP, and glycinebetaine (GB) are essential for been studies that have focused on evaluating producing abalone flavor.19 Although there is a lack metabolic stress during air exposure in live paua of data about GB, these components are known to Haliotis iris and H. australis,9,10 and in live clams be present in abundant amounts in the small Paphies donacina,11 it is not clear how these abalone muscle.3 It has also been reported that in changes in the metabolites measured affect the abalone and meat of kuruma prawn,2,20 and organoleptic qualities. As described by Olley and in the soup of hard clam21 heating at different con- Thrower, the extractive components and meat ditions results in a significant change in the pre- quality of abalone might be influenced by hand- ference of sensory properties, and that higher ling conditions prior to death.12 amounts of extractive components have been detected in preferred samples. There is no information available about the *Corresponding author: Tel: 886-2-2462-2192 ext. 5114. changes in freshness indices and extractive com- Fax: 886-2-2463-4203. Email: [email protected] ponents of live small abalone during storage. The Received 19 February 2001. Accepted 23 August 2001. present study investigates the changes in pH, Changes of extractive component in small abalone FISHERIES SCIENCE 381

volatile basic nitrogen (VBN), K-value, glycogen, AMP, IMP (inosine monophosphate), inosine adenosine triphosphate (ATP) and its related com- (HxR), adenosine (Ado), and hypoxanthine (Hx), pounds, and free amino acids in the foot muscle of were extracted with 6% perchloric acid, and ana- live small abalone during storage at 5∞C, 15∞C, and lysed by high performance liquid chromatography 25∞C. as described elsewhere.8 The K-value (%)was then calculated using the following equation:24

MATERIALS AND METHODS [(HxR + Hx)/ (ATP + ADP + AMP + IMP + HxR + Hx)] ¥ 100 (1) Samples

Cultured live small abalone Haliotis diversicolor Free amino acids that had been fed gracilar Gracilaria sp. were col- lected three times in November and December Using the method of Konosu et al., a trichloroacetic 1997 from culture farms in the north-eastern area acid (TCA) extract was prepared using 10 g of of Taiwan. The samples (shell length 5.4 ± 0.4 cm, muscle as the starting material.25 The contents of bodyweight 17 ± 3 g) were transported within 1.5 h free amino acids (FAA) in the TCA extract were to the laboratory and acclimated in aerated seawa- determined with a L-8500 high-speed amino acid ter at ambient temperature for 2 h prior to use. The analyser (Hitachi, Tokyo, Japan). The method used live specimens were then divided into three groups is described elsewhere.8 and stored separately at 5∞C, 15∞C, and 25∞C. At regular intervals, five specimens were taken from each group and each foot muscle removed. The Sensory test muscles were pooled, cut into small pieces, mixed well, and taken as the sample for subsequent Sensory tests were conducted according to the analyses. A muscle sample of approximately 5 g method of Watanabe et al.26 The degree of freshness was used unless otherwise stated. of stored small abalone muscles was evaluated by laboratory panelists who had been trained previously to familiarize themselves with the Volatile basic nitrogen characteristic odor of acceptable and unaccept- able samples. Based on odour, freshness was The volatile basic nitrogen content (mg/100 g) in classified into three stages: (i) acceptable (no samples was determined by the microdiffusion putrid smell); (ii) initial decomposition (faintly method of Cobb et al.22 putrid smell); and (iii) advanced decomposition (putrid smell). pH value RESULTS AND DISCUSSION The muscle homogenate was prepared in distilled water in a ratio of 1 : 10 (w/v). The pH of the Freshness indices and glycogen homogenate was measured using a CG-840 pH meter (Scott, Hofheim, Germany) at room The initial levels of pH, VBN, and K-value in the temperature. foot muscle of small abalone were 6.57 ± 0.02 (mean ± SD), 2.6 ± 0.9 mg/100 g, and 2.4 ± 1.1%, respectively (Fig. 1). According to the sensory Glycogen rating test, the onset of initial decomposition was observed after 3.5 days at 5∞C, after 2.5 days at Glycogen in the muscle samples (mg/100 g) was 15∞C, and after one day at 25∞C. The shelf-life of extracted and measured using the colorimetric small abalone was short compared with those of method described by Carroll et al.23 hard clam Meretrix lusoria and abalone Haliotis discus.8,26 In the present study live small abalone were used initially for the storage experiments. Adenosine triphosphate and its However, they gradually lost activity during related compounds storage and finally became unresponsive when their foot muscles were gently tapped with a Adenosine triphosphate and its breakdown prod- spatula. Although the change in mortality during ucts, including adenosine diphosphate (ADP), storage was not monitored, all specimens at the 382 FISHERIES SCIENCE T-K Chiou et al.

Fig. 1 Changes in levels of () pH, () volatile basic nitrogen (VBN), and () K-value in the foot muscle of small abalone during storage at 5∞C, 15∞C, and 25∞C. Data are the mean ± SD of triplicate experiments. Arrows indicate the time of onset of initial decomposition (2) and advanced decomposition (3).

initial decomposition stage were unresponsive. Watanabe et al. have demonstrated that starved disk abalone have a better survival rate during air exposure than fed abalone.27 In agreement with the findings for the scallop species Patinopecten yessoensis and Placopecten magellanicus,28,29 and for New Zealand abalone,9 the pH values in the foot muscle of small abalone declined with storage time (Fig. 1). The VBN content and K-value increased gradually or steadily during storage at 15∞C and 25∞C, but rates were slow at 5∞C except for a sudden rise in the K-value that occurred after 3.5 days. The K- value ranged between 11.6% and 13.1% at the initial decomposition stage. The initial amount of glycogen was 1826 ± 147 mg/100 g. Glycogen tended to decrease during storage, and the Fig. 2 Changes in the levels of glycogen in the foot decrease at 15 C seemed to be slower than at muscle of small abalone during storage at ( ) 5°C, ( ) ∞ 5∞C (Fig. 2). Summers et al. have examined the 15°C, and ( ) 25°C. Data are the mean ± SD of triplicate effect of storage temperature on stress in live clams experiments. stored at 0∞C and 4∞C, and concluded that storage at 0∞C results in a greater reliance on anaerobic glycolysis to maintain their energy status.11 A for abalone.26 It has been reported that Hx content decrease in glycogen during storage was also found is a useful index of quality for scallop.29,30,34 The K¢ in the hard clam,8 Japanese baking scallop,30 and value, which is calculated from the following periwinkle Tympanostomus fuscatus.31 However, equation:35 glycogen in the New Zealand abalone9 and the [(IMP HxR Hx)/ mussel Mytilus galloprovincialis32 showed no sig- + + (ATP ADP AMP IMP HxR Hx)] 100 (2) nificant variation within 24 h and 36 h of anoxia, + + + + + ¥ respectively. is also reported to be a more appropriate freshness The alternation patterns of K-value and VBN index for shellfish because the K¢ value increases observed in the present study were similar to those faster than the K-value.33,35,36 Similar to abalone,26,33 of the abalone muscle stored at 5∞C and 10∞C.26,33 IMP has been detected in low amounts in small Watanabe et al. have demonstrated that the K- abalone, and its levels change little during storage value and VBN are not applicable freshness indices (Fig. 3). Changes of extractive component in small abalone FISHERIES SCIENCE 383

Fig. 3 Changes in the level of adenosine triphosphate (ATP) and its related compounds in the foot muscle of small abalone during storage at 5∞C, 15∞C, and 25∞C. Data are the mean ± SD of triplicate experiments. Bars at the top of each column indicate the SD of the total content. ADP, adenosine diphosphate; AMP, adenosine monophosphate; IMP, inosine monophosphate; HxR, inosine; Ado, adenosine; Hx, hypoxanthine.

Adenosine triphosphate and its storage followed two routes: (i) AMP Æ Ado Æ HxR related compounds Æ Hx; and (ii) AMP Æ IMP Æ HxR Æ Hx. The data might also suggest that the former was generally a Figure 3 shows changes in the levels of ATP and its key route, while the latter proceeded slowly unless related compounds (ARC). The total amount of at elevated temperatures. In the present study it is ARC was 3.62 ± 0.11 mmol/g before storage. The noted that the rate of ATP degradation, especially total amount of ARC increased slightly after in the early period of storage, was faster than that storage, and was possibly related to the moisture of the shucked disk abalone muscle as reported by lost after storage and variation among the original Watanabe et al.26 The investigators have indicated fresh samples (0 day). The ATP compound was that the rate of ATP degradation in disk abalone is most predominant (1.60 ± 0.17 mmol/g), followed slower than in other invertebrates, and on the first by ADP (1.22 ± 0.08 mmol/g) and AMP (0.64 ± 0.14 day of storage at 5∞C and 10∞C ATP produced in the mmol/g). Low amounts of IMP, Ado, HxR, and Hx muscle was more than that consumed. In addition, were detected (0.03–0.08 mmol/g). Levels of ATP prolonged accumulation of AMP with quantita- decreased rapidly during the first half day of tively large proportions in the total amount of storage, and the rate at 5∞C was slower than the ARC was observed (Fig. 3). This might be a special rate at 15∞C and 25∞C. Levels of ADP declined after feature in the storage of live small abalone because half a day of storage, but slowed during the sub- the AMP content in abalone muscle increased sequent period. In contrast, AMP increased in the linearly with storage period up to 10 days at 5∞C,33 same time period, and then remained almost or increased to a maximum and subsequently constant at around 3.0–3.3 mmol/g (an average of decreased during storage at 0–10∞C.26 The AMP 76% of the total amount of ARC) prior to the initial compound has been confirmed as a taste-active decomposition of the samples. Accompanying component in abalone,19 snow crab,16 scallop,17 the breakdown of nucleotides, the accumulation of and shorted-necked clam.18 Also, the amount of Hx was higher than that of Ado and HxR. Their AMP, which varies with different cooking con- average contents, in decreasing order, reached ditions, has been reported to be a factor related 0.33–0.38 mmol/g, 0.17–0.20 mmol/g, and 0.09– to taste preference for the prawn muscle20 and 0.21 mmol/g at the initial decomposition stage, in soup of hard clam.21 which the HxR content was larger at 25∞C than at 5∞C and 15∞C. The alternation patterns of ARC obtained by the Free amino acids present study demonstrated, similarly to abalone26 and other marine invertebrates,33,36,37 that AMP Results of the changes in level of FAA are shown in degradation in the muscle of small abalone during Table1. The dominant constituents in all samples 384 FISHERIES SCIENCE T-K Chiou et al. 71 1 5 2 1 0 1 0 2 2 1 1 1 1 2 0 1 3 54 3 1 8 9 3 1 0 134 1 206 ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± 3.5 2 8 1 8 6 3 1 14 47 35 441 21 21 35 11 01 02 02 36 21 38 26 04 32 27 02 13 43 75 258 11 18 12 12 72 31 23 91 1333 17 130 2288 ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± 3.0 4 0 4 0 1 7 3 7 55 455 11 22 05 11 00 12 12 09 31 21 17 04 33 28 12 13 24 56 253 41 56 11 21 10 51 43 21 24 4 1390 16 92 2398 ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± 6 2 0 4 9 8 5 6 2.5 12 514 41 32 34 10 00 12 12 11 11 29 16 15 15 28 02 22 43 83 265 41 17 10 18 20 55 83 51 14 132 1516 07 170 2602 ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± 2.0 C storage (days) 5 ∞ C storage 53 471 314 120 25 11 00 02 12 19 313 29 16 24 13 38 12 13 341 46 279 120 19 820 14 53 330 217 13 70 1405 16 123 2455 ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± 3 6 3 1 0 6 7 9 5 1.5 12 456 31 51 34 11 00 02 12 28 11 31 07 24 13 11 13 03 63 58 297 51 08 12 18 14 44 52 21 04 25 1296 16 144 2327 ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± 1.0 21 456 313 416 04 01 00 12 12 09 113 29 16 05 02 28 03 22 840 51 273 416 18 820 10 43 627 217 13 55 1329 06 92 2332 ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± 0 6 1 9 5 7 4 4 3 368 236 8 21 21 24 11 00 02 02 17 21 28 26 15 12 27 13 13 72 71 41 17 61 93 12 01 34 74 1096 05 157 1934 ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± 3 1 0 1 1 6 7 5 3 3 6 2 1 6 8 5 10 14 11 28 13 16 31 20 13 388 221 1317 2142 Changes in level of free amino acids (mg/100Changes in level of free g) in the foot muscle of small abalone during storage Arginine Histidine Lysine Ornithine Ethanoamine g -ABA b -AiBA b -Alanine Phenylalanine Tyrosine Leucine Isoleucine Cysthionine Methionine Valine a -ABA Citrulline Alanine Glycine Proline a -AAA Glutamine Glutamic acid Glutamic Serine Threonine Aspartic acid Taurine Phosphoserine Table 1 Amino acids storage Before 0.5 Total Changes of extractive component in small abalone FISHERIES SCIENCE 385 155 51 1 3 2 1 3 0 1 1 2 0 1 1 2 1 4 1 2 77 4 7 2 9 14 74 2 1 1 ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± 1.5 313 2622 42 529 515 319 11 110 01 14 13 215 211 211 23 15 18 210 03 26 10 49 74 339 222 813 07 730 20 55 419 195 1420 12 011 ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± 1.0 C storage (days) ∞ C storage 25 176 2364 52 482 313 618 11 14 01 03 03 213 38 39 23 05 17 18 13 641 13 60 280 916 18 11 12 527 11 52 414 67 1315 03 09 ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± 0.5 41 2330 21 467 314 318 01 18 3 00 13 02 212 19 18 14 15 26 48 22 641 53 51 282 220 19 10 16 227 14 51 34 1294 316 02 17 ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± 3.5 68 2449 01 323 01 14 13 213 23 458 28 413 19 13 05 17 319 19 02 848 19 90 298 519 17 813 223 16 51 314 01 112 30 1377 ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± 3.0 g -amino- n -butyric acid. g -ABA, 170 2350 15 474 314 520 10 46 01 13 12 311 27 09 12 35 17 18 03 547 24 96 275 318 17 613 529 17 54 313 65 1310 11 19 ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± 2.5 56 2646 46 530 315 621 11 37 01 03 12 315 29 22 15 27 310 39 13 752 24 66 294 720 29 11 14 54 1484 17 65 516 10 34 02 110 ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± 2.0 b -amino-isobutyric acid; 150 2339 12 462 413 420 11 44 01 12 02 313 28 23 13 27 29 38 12 12 67 275 10 42 519 27 11 14 331 14 54 316 12 24 1311 17 b -AiBA, ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± 1.5 C storage (days) 15 ∞ C storage 208 2297 77 448 613 719 01 16 00 12 12 114 38 23 34 16 28 18 13 14 543 18 300 218 918 352 724 215 115 1262 28 17 13 ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± 1.0 a -amino- n -butyric acid; 11 33 00 02 02 218 2176 38 64 443 313 13 14 16 29 27 519 13 213 18 739 43 248 415 13 647 17 728 24 314 11 16 82 1213 ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± 0.5 4 2 0 1 3 4 5 7 6 2 6 3 10 15 11 29 15 23 13 16 380 245 1995 1141 SD of triplicate experiments. ± Continued a -amino adipic acid; -ABA, Data are the mean are Data a -AAA, Total Arginine Histidine Lysine Ornithine Ethanoamine 1 b -AiBA g -ABA b -Alanine Phenylalanine 6 Tyrosine Methionine Cysthionine Isoleucine Leucine Valine a -ABA Citrulline Alanine Glycine Proline a -AAA Glutamine Glutamic acidGlutamic 35 Serine Threonine Aspartic acid 4 Taurine Table 1 Amino acids Phosphoserine 5 386 FISHERIES SCIENCE T-K Chiou et al.

were Tau, Arg, Gly, Glu, and Ala. The quantities of amounts of those amino acids responsible for these five amino acids increased during storage. taste, a slow rate of AMP degradation, and a short Several amino acids such as serine, proline, lysine, shelf-life. Alternatively, an immediate decrease in and histidine, also exhibited a slight increase. Con- the levels of ATP and ADP (Fig. 3), but no apparent sequently, the total amount of FAA increased after change in glycogen (Fig. 2), were also found during storage except for those samples stored for half a the early days of storage. The results imply that day at 5∞C and 15°C, in which the total amount small abalone stored out of seawater could not suf- slightly declined. During the early days of storage ficiently maintain enough energy from anaerobic at 5∞C and 15∞C, increases in the total amount of glycolysis catalysed by pyruvate reductases.11,38 FAA were slower than at 25∞C. During the first half day of storage at 25∞C, Glu, Gly, Ala, and Arg increased rapidly, but Tau remained unchanged. ACKNOWLEDGMENT In agreement with the total amount of FAA, the highest levels of Tau, Glu, and Arg were observed This research was supported by a grant (NSC-89- 2.5 days after storage at 5∞C and 15∞C. Conversely, 2313-B-019-016) awarded by the National Science Gly showed a maximum after only 1.5 days of Council, Taiwan. storage at these temperatures, and then fell during storage at 5∞C but not at 15∞C. The amount of Ala increased slightly after one day of storage, and REFERENCES fluctuated thereafter during storage at 5∞C, but 1. Wells RMG, Baldwin J. A comparison of metabolic stress exhibited a continuous rise during the first 2.5 days during air exposure in two species of New Zealand abalone, of storage at 15∞C. 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