Quality and Shelf Life of Cold and Frozen Rainbow Trout (Oncorhynchus mykiss) Fillets: Effects of Fish Protein-Based Biodegradable Coatings

The Klunzinger’s ponyfish (Equulites klunzingeri) protein powder extracted with acid or alkali aided process as a biodegradable coating material for rainbow trout (Oncorhynchus mykiss) fillets during cold (+2°C) and frozen storage (–18°C) were investigated. The coating with alkaline treated protein (AlPC) and acid treated protein (AcPC) extended the shelf life of fillets from 11 to 14 days in cold storage and improved the quality parameters in three months frozen storage period. According to total viable count and total psychrophile count results, bacteria grew more quickly in uncoated fillets than coated fillets. The protein-based coating did prevent spoilage of the rainbow trout fillets as reflected by a decrease in pH, total volatile base-nitrogen and free fatty acids during cold and frozen storage period. Therefore, this study demonstrated that fish protein-based coating had a positive effect on maintaining the rainbow trout fillets quality, and edible coatings from discard fish can offer a promising alternative for preserving fish fillets.     

Impact of Wall Materials on Physicochemical Properties of Microencapsulated Fish Oil by Spray Drying

The aim of the present study was to investigate the effect of wall materials composition on physicochemical characteristics of fish oil microcapsules produced by spray drying (180 °C). Four different combination of coating materials (fish gelatin, chitosan, combination of gelatin and chitosan, and a mixture of microbial transglutaminase (MTGase) with maltodextrin) were applied to two different fish oils to produce 40 % solid emulsions. Scanning electron microscopy and extraction of surface and encapsulated oils revealed that fish gelatin provided the highest preserving effect on the covering fish oil. Meantime, addition of MTGase to gelatin could also increase this ability and reveled less surface oil than chitosan treatment (2.63 and 2.80 % versus 4.66 and 5.23 %, respectively; P?<?0.05). Mixture of gelatin and maltodextrin with MTGase as wall material led to the highest encapsulation efficiency, being selected as the best microencapsulation condition; meantime, application of chitosan with maltodextrin provided the worse encapsulation efficiency (P?<?0.05). All indices of powders (encapsulation efficiency, surface morphology, and particle size) showed that powders prepared from gelatin and gelatin with MTGase increased the encapsulation efficiency and would increase the stability of microcapsule powders.     

优势腐败菌对暗纹东方鲀冷藏期间品质变化影响及致腐能力分析

为分析暗纹东方鲀(Takifugu obscurus)优势腐败菌的不同接种方式对其冷藏期间品质变化影响及致腐能力.将荧光假单胞菌(Pseudomonas fluorescens)、腐败希瓦氏菌(Shewanella putrefaciens)分别以单一和联合法接种到无菌整鱼上,依次分为荧光假单胞菌接种(P.fluore...     

Effects of an edible coating, fungicide and cold storage on microbial spoilage of cherries

The effects of an edible coating, i.e., Semperfresh^TM, fungicide, i.e., Imazalil, and cold storage on microbial spoilage of cherries were studied. Two group of cherries (Prunus avium) were coated just after harvest with 1% and 2% Semperfresh^TM fruit coating. Two other group of cherries were treated with 75 ppm and 150 ppm concentrations of Imazalil and then coated with a 1% concentration of Semperfresh^TM fruit coating. Half of the cherries from each of the above groups was stored at ambient temperature (~30Dž °C) and at 40-50% relative humidity, the other half of the cherries was stored at cold storage (0 °C) and at 95-98% relative humidity. Each group was analyzed for the mold and yeast count. The Semperfresh^TM edible coating resulted in a slightly increased fungal spoilage of fruits. Imazalil fungicide treatment clearly decreased and retarded the microbial spoilage of fruits. As a result, low temperature storage was the most effective solution for both microbial spoilage and delay in the ripening.     

Effects of Bromelain Tenderisation on Myofibrillar Proteins,Texture and Flavour of Fish Balls Prepared from Golden Pomfret

An enzymatic method to tenderise golden pomfret (GP, Trachinotus blochii) flesh by marinating with bromelain (BML) solution was developed to produce GP fish balls with a texture similar to those of yellowtail fusilier (YF, Caesio cuning). Treatment with BML reduced the hardness, chewiness and gel strength significantly but increased the resilience of GP fish balls. As a result, 0.4% (enzyme-substrate ratio, w/w) BML-treated GP fish balls had the same texture properties as YF fish balls. Meanwhile, changes in myofibrillar proteins in the fish balls were determined using sodium dodecyl sulphate polyacrylamide gel electrophoresis, matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry and atomic force microscopy. The results indicated that BML degraded myosin light chain and troponin T effectively, without affecting actin. BML treatment generated protein fragments with significantly smaller sizes, thereby improving the tenderness of the flesh. The length, width and height of the myofibrils from 0.4% BML-treated fish ball were 6.42, 1.52 and 1.48 μm, respectively, which were not significantly different from the myofibrils of YF fish balls, indicating that the similar nanostructure determined the comparable texture properties. Gas chromatography-mass spectrometry analysis showed that 0.4% BML decreased the amount of hexanal, hexadecane, 1-octen-3-ol and 2,6,10,14-tetramethylpentadecane but increased the ratio of heptadecane from 18.14 to 38.23% in the treated fish balls, making the flavour of 0.4% BML-treated GP fish balls similar to that of YF balls. Overall, the results suggest that 0.4% BML-tenderised GP could be a promising alternative to YF to produce quality fish balls.     

Edible Antimicrobial Coating Incorporating a Polymeric Iron Chelator and Its Application in the Preservation of Surimi Product

To explore a novel efficient method in food preservation, edible zein coating which incorporates a polymeric chelator was developed and its preservative effect on commercially manufactured fish balls was investigated. The quality indicators of the fish ball during the storage, including sensory quality, total bacterial count, total basic volatile nitrogen (TVB-N) content, thiobarbituric acid reactive substances (TBARS), and pH value were determined. It has been demonstrated that a zein film containing a polymeric chelator significantly (P?<?0.05) improves the sensory properties, retards the growth of spoilage bacteria, and decreases TVB-N and TBARS values. The increase of the microbial load of fish balls coated with antimicrobial zein during a 16-day refrigeration storage period was less than 1 log cfu/g, while the microbial load increased to about 5 log cfu/g for the control group lacking the coating treatment. Although statistically significant differences in the pH values were not observed between coated and uncoated fish balls (P?>?0.05), fish balls coated with antimicrobial zein maintained a relatively stable state during storage. Zein coating which incorporates a polymeric chelator extends fish ball shelf life to 19 days at 4 °C, being more efficient than zein coating lacking a polymeric chelator (13 days). Clearly, polymeric chelator-incorporated zein film could find application in the preservation of surimi products by preventing the growth of bacteria and oxidation of fat during storage.     

Effect of anchovy by-product protein coating incorporated with thyme essential oil on the shelf life of anchovy (<Emphasis Type="Italic">Engraulis encrasicolus</Emphasis> L.) fillets

The effects of anchovy by-product protein coatings incorporated with thyme essential oil (TEO) on the shelf life of anchovy (Engraulis encrasicolus L.) fillets stored at 4 ± 1 °C were investigated. We grouped fillets in three categories: untreated fillets, fillets treated in coating solution alone, and fillets treated in coating solution containing 1.5% TEO and analyzed on 0, 3, 6, and 9 days of storage. It was observed that the total volatile basic nitrogen (TVB-N) and pH of all the fillet groups increased under cold storage conditions; however, this increase was much slow in both the coated anchovy fillets. Both coating applications slowed down the lipid oxidation but the coating containing TEO exhibited better effect than coating alone. The coating application alone or with essential oil had limited effect on microbial growth but positively affected the sensory quality. These results revealed that anchovy by-product protein coating mixed with TEO may prolong anchovy fillets’ shelf life stored under cold condition.     

鱼鳞明胶及蛋白肽涂膜对鲫鱼保鲜效果的影响

研究鱼鳞明胶和蛋白肽涂膜剂对鲫鱼保鲜效果的影响。将明胶、蛋白肽、壳聚糖混合制成涂膜剂,涂布在鲫鱼鱼片的表面,在4℃环境下存储,每隔一段时间进行1次测定,分别检测鲫鱼鱼片的p H值、重量损失、TVB-N、菌落总数、色差等指标,以检验混合膜对鲫鱼的保鲜效果。经过15天的存储,明胶、蛋白肽、壳聚糖涂布鱼片表面,能延长鱼片的保质期。试验证明明胶、蛋白肽在鲫鱼鱼片保鲜中的可行性和保鲜效果。     

Effects of Vacuum Packaging and Wrapping with Chitosan-Based Edible Film on the Extension of the Shelf Life of Sea Bass (Dicentrarchus labrax) Fillets in Cold Storage (4 °C)

In the present study, we assessed the possibility of improving the shelf life of fresh sea bass (Dicentrarchus labrax) fillets by using vacuum packaging and wrapping with chitosan-based edible films during cold storage at 4 °C. Sea bass fillet samples were periodically evaluated to assess chemical (pH, trimethylamine and total volatile basic nitrogen) and microbiological (presence of mesophilic aerobic bacteria and psychrotrophic bacteria) quality. Chemical spoilage (trimethylamine and total volatile basic nitrogen) and growth of microorganisms (total mesophilic and total psychrophilic aerobic bacterial counts) were significantly reduced (P?≤?0.05) in vacuum-packaged chitosan film wrapping during cold storage at 4 °C. The results showed that the shelf life of the control and vacuum-packaged groups ended within 5 days, whereas that of vacuum-packaged chitosan film-wrapped samples ended at 25 to 30 days. Therefore, the shelf life of sea bass fillets wrapped in chitosan was prolonged by about 20 days.     

Influence of Rice Bran Wax Coating on the Physicochemical Properties and Pectin Nanostructure of Cherry Tomatoes

The effects of rice bran wax coating on the physicochemical properties such as firmness, weight loss, titratable acidity (TA) and soluble solid content (SSC) of cherry tomatoes were studied during cold storage. The chemical and nanostructure properties of chelate-soluble pectin (CSP) were also investigated by high-performance liquid chromatography (HPLC), Fourier transform infrared spectroscopy (FTIR) and atomic force microscopy (AFM). The results indicated that there was no significant difference of firmness between control (2.48 N) and waxed (2.87 N) fruits at the end of storage (20 days), while the weight loss of waxed fruits (13.54%) was lower than that of control fruits (16.02%). And the degree of esterification (DE) of both fruits decreased after cold storage by FTIR. The structural analysis by atomic force microscopy (AFM) indicated that rice bran wax coating inhibited the degradation of CSP. The CSP molecular widths ranged from 15 to 250 nm, and the vertical heights varied from 0.2 to 2.0 nm. Greater frequency (F _q ) of large width and length CSP was found in waxed fruits than in control fruits. The results suggest that rice bran wax coating was an effective way to preserve fresh fruits.     

USING GELATIN-BASED ANTIMICROBIAL EDIBLE COATING TO PROLONG SHELF-LIFE OF TILAPIA FILLETS

Skinless tilapia (Dreochromis niloticus x D. aureus) fillets were covered with a gelatin coating containing benzoic acid as an antimicrobial agent. Benzoic acid content of fish fillets was used to estimate the amount of gelatin coated on fillet surface, and it was found that the gelatin contents were between 16.3 mg and 17.3 mg per g of fillets. Aerobic and anaerobic microbial loads, volatile basic nitrogen (VBN) contents, and sensory evaluation were used as indicators to survey the feasibility of an antimicrobial gelatin coating to prolong the shelf‐life of tilapia fillets under refrigeration. After 7 days of storage under refrigeration, tilapia fillets coated with gelatin containing benzoic acid had acceptable VBN contents, increased moderately in microbial loads, and showed no significant sensory difference (P < 0.05) from fresh fillets. The results indicate that an antimicrobial gelatin coating is suitable for preservation of tilapia fillets.     

Effect of gelatin coating incorporated with cinnamon oil on the quality of fresh rainbow trout in cold storage

Cinnamon essential oil was used in gelatin coatings to maintain the quality of refrigerated rainbow trout fillets over a period of 20 days. Fish fillets were coated with a solution of 4% gelatin incorporated with cinnamon essential oil and then stored in refrigerator (4 ± 1 °C). Coating’s preservative effect was assessed periodically (every 5 days) by microbial analyses (aerobic plate count and psychrotrophic count), chemical determinations (total volatile basic nitrogen, thiobarbituric acid, free fatty acid) and sensory characteristics. When gelatin coating with cinnamon applied to the preservation of trout fillets, a reduction in the growth of total bacteria was observe after 15 days of storage. Fish fillets with gelatin coating containing 1%, 1.5% and 2% v/v cinnamon oil produced significantly lower (P < 0.05) total volatile basic nitrogen then gelatin‐coated fillets and control until 15 days of storage period (35, 22.86, 30.33, 57.76 and 53.26 mg per 100 g of fillet, respectively). The obtained results indicate that gelatin in the form of coating enriched with cinnamon oil is suitable for the preservation of rainbow trout fresh fillets and to efficiently maintain the quality attributes to an acceptable level during storage.     

Dual bacterial strains TTI for monitoring fish quality in food cold chain

Most microbial time–temperature indicators (TTIs) considered only one spoilage strain. This research compared single and dual spoilage strains-based microbial TTI for quality changes of chilled grouper fish (Epinephelus fuscoguttatus x E. lanceolatus) fillet products during distribution. The next-generation sequencing (NGS) and traditional plate count approach showed that Pseudomonas fragi and Vibrio parahaemolyticus were specific spoilage bacteria at 7 and 15°C. A dual-strain TTI response provides more accurate results than a single-strain TTI and provides an irreversible color change from yellow to reddish-brown, showing levels of fish freshness. The microbial TTI comprises fish spoilage bacteria strains with 3 log CFU/ml, a nutrient broth supplemented with 2% NaCl as a medium, and phenol red with 0.25 mg/ml as a pH indicator. Overall, this study points to the applicability of a dual-strain microbial TTI as a valuable tool for monitoring fish quality changes during cold chain break condition.     

预调理冷藏罗非鱼片保藏技术

为提高冷鲜罗非鱼的保藏货架期,文中采用化学保鲜剂对罗非鱼进行宰前减菌化处理,再用生物保鲜剂结合香辛料对鱼片进行预调理,并于冷藏(10℃)条件储藏8 d,期间测定鱼片的菌落总数、挥发性盐基氮、pH值,并进行感官评价。实验结果表明:罗非鱼宰杀前用50 mg/L的稳定态ClO2浸泡10 min可将罗非鱼体表肉菌落总数由8.6×104CFU/g降低至2.4×103CFU/g,减菌率达97.21%;3种生物保鲜剂均可延长鱼片的货架期,其中,0.01%的纳他霉素的保鲜效果较好,鱼片较对照组延长了2～3 d。香辛料预调理不能显著延缓鱼肉的腐败变质,但与生物保鲜剂有一定的协同作用,尤其是在改善鱼肉色泽等感官指标的劣变方面较明显;经香辛料调理后的冷鲜罗非鱼片具有自然、纯正的鱼香味,无鱼腥味,麻辣适中,口感鲜美。     

壳聚糖复合保鲜对草鱼肌肉品质变化的影响

为探讨有效的冷鲜草鱼保鲜技术方案,分别以壳聚糖复合保鲜液（10 mg/mL壳聚糖＋5 mg/mL茶多酚＋2 000 U/mL溶菌酶）和无菌水（对照组）处理草鱼片,通过对比草鱼冷藏过程中鲜度（K值）、ATP关联物含量、汁液流失率、质构特性、挥发性气味等指标的变化情况,分析壳聚糖复合保鲜对草鱼肌肉品质变化的影响。结果表明：冷藏过程中,草鱼肉的K值、次黄嘌呤含量、汁液流失率、黏附性和挥发性物质随时间延长有不同程度增加,但保鲜组样品的增幅明显小于对照组;对照组草鱼的肌苷酸含量和硬度随时间延长逐渐下降,而保鲜组则先上升后下降,且下降变化率明显低于对照组。说明壳聚糖复合保鲜液对草鱼保鲜效果较好,能有效延缓鱼肉的品质劣变进程。     

Oxidatively Derived Volatile Compounds in Microencapsulated Fish Oil Monitored by Solid-phase Microextraction (SPME)

The stability of microencapsulated fish oil was studied during storage at 4 °C for up to 20 wk. Different coating mixtures consisting of gelatin or caseinate in blends with carbohydrates (sucrose, lactose, maltodextrin) were investigated. Oxidative stability of the microencapsulated fish oil was monitored by analysis of volatile compounds using gas chromatography olfactometry (GC‐O) or GC flame ionization (GC‐FID) (SPME‐HS‐GC/O or GC/ FID and HS‐GC/MS), Oxipres test, thiobarbituric acid‐reactive substances (TBARS), and sensory analysis. Coating mixture of caseinate and lactose showed slightly better stability than the sucrose and maltodextrin caseinate mixtures. Combination of fish gelatin and maltodextrin did not show as good oxidative stability as the coating blend of caseinate, lactose, and lecithin. Hexanal, 2‐nonenal and 2,4‐decadienals were selected as quality indicators to monitor the lipid oxidation during storage of the samples. SPME‐GC‐O analysis of these indicators showed that they were representative for the oxidation occurring in the microencapsulated fish oil. SPME‐GC‐FID analysis was sensitive enough to detect oxidative changes during storage. Oxidative stability test, TBARS results, and sensory analysis were in agreement with the SPME, indicating that SPME (polydimethylsiloxane/divinylbenzene [PDMS/ DVB] fiber) can be a useful tool for rapid analysis of lipid oxidation in microencapsulated fish oil.     

Thawing, Refreezing and Frozen Storage Effects on Muscle Functionality and Sensory Attributes of Frozen Cod (Gadus morhua)

Thawing and re-freezing of cod fillet blocks did not necessarily result in greater deterioration (relative to a ‘once frozen’ control) of cooked fish sensory attributes after 9 months frozen storage at –22°C. Thawed and refrozen fish muscle displayed a faster decline in myofibril protein solubility than once frozen controls and had reduced water-holding capacity but analysis of proton spin-spin relaxation times indicated no change in water location. The decline in protein solubility was not caused by complete protein unfolding. Long thawing times (30 hr) before re-freezing and storage resulted in cooked fish with more gray appearance and more stale flavor. Changes in fish muscle functionality did not enable direct inference of sensory attributes.     

冷链物流中海水鱼的腐败机制及保鲜技术研究进展

海水鱼营养成分丰富、水分含量高,在冷链物流中容易发生腐败变质。因此,通过了解冷链物流中海水鱼的腐败机制并有针对性地开展海水鱼产品保鲜,进而提升冷链物流中海水鱼产品品质。作者论述了海水鱼冷链物流中的自溶性腐败、氧化腐败和微生物腐败机制,并重点阐述了控制微生物腐败的保鲜技术研究进展。通过臭氧水、电解水、低温等离子体、辐照杀菌、高静压杀菌技术、光动力杀菌技术等减菌技术,可有效减少海水鱼表面微生物;采用温度控制、气调包装、活性包装等可有效控制冷链物流中海水鱼的微生物增长、蛋白质和脂质氧化,从而控制海水鱼的腐败变质,维持海水鱼的鲜度品质。这些研究发现可为进一步开发应用于冷链物流中海水鱼的保鲜技术提供借鉴和参考。     

Storage Quality of Fresh and Frozen-thawed Fish in Ice

The objective was to determine whether traditional quality indexes of fresh (unfrozen) fish like sensory analysis, bacterial counts and trimethylamine content could be applied to thawed whole cod, cod fillets and ocean perch fillets kept in ice. Freezing and short-term freezer storage (≤5 wk at ?25°C) had very little effect on bacterial counts. During long-term freezer storage (≥14 wk at ?25°C) total counts were reduced as well as counts of trimethylamine oxide-reducing bacteria in cod fillets but not in ocean perch fillets. When the thawed fish was unacceptable the trimethylamine was <1 mgN/100g. Trimethylamine as a spoilage indicator was of no value when evaluating spoilage of thawed whole cod, cod fillets and ocean perch fillets kept in ice.     

Effect of Crystalline Structure on Oxidation of Fish Oil in Stearin:Fish Oil Mixtures

Effects of incorporation of stearin fraction into fish oil on crystallisation behaviour and oxidative stability of fish oil were examined. The stearin fraction (S₂₅) was obtained from step-wise dry fractionation of anhydrous milk fat at 25 °C. Analysis of fatty acid composition by gas chromatography showed that unsaturated fatty acids (89.3 %) were enriched in the fish oil whereas the S₂₅ typically comprises of saturated fatty acids (79.4 %). A series of S₂₅:fish oil mixtures (0:100, 25:75, 50:50, 75:25; 90:10 and 100:0) was prepared by mixing the S₂₅ and fish oil at 50 °C under flushing of nitrogen gas. Crystallisation and thermal properties and crystal structures of the mixtures were investigated by differential scanning calorimetry and small- and wide-angle X-ray scattering, respectively. The crystallisation/melting temperatures and crystallisation/melting enthalpies of the mixtures increased with increasing ratios of S₂₅ blended into fish oil. All mixtures showed similar crystal structures (double- and triple-chain length) and crystal polymorphs (α, β’ and β) at 4 °C. A decrease in S₂₅ fraction in the mixtures caused a higher proportion of triple-chain length crystal packing and β polymorph. Measurement of peroxide values of the mixtures upon storage at 8 °C for 42 days showed that blending as low as 25 % S₂₅ sufficiently delayed the lipid oxidation of fish oil by about two-fold and the rancidity threshold to 16 days instead of 9 days for fish oil only. This study demonstrates that mobility of oxygen and triacylglycerol (TAG) molecules in fish oil can be restricted by crystalline state of milk fat, in turn, limiting the propagation of oxidative reaction in fish oil.