Drying Kinetics and Quality Characteristics of Slightly Salted Grass Carp Fillets by Hot Air Drying and Vacuum Microwave Drying

Salted grass carp fillets were dried by hot air drying (HD, at 35 and 45°C) and vacuum microwave drying (VMD, at 1, 4, and 7 W/g) to a final moisture content. Compared with hot air drying, the vacuum microwave drying greatly reduced drying time. The rehydration rate constant of salted grass carp fillets dried by microwave vacuum drying at 7-W/g microwave intensity was significantly higher than that of the hot air drying at 35 and 45°C. Compared with hot air drying, the vacuum microwave dried samples had a higher crude fat content (dry basis). The lightness of the samples dried by vacuum microwave drying was higher, and the yellowness was lower than those dried by hot air drying. The drying methods had no significant effect on the hardness and springiness.     

Textural and Sensory Properties of Herring (Clupea harengus) Cubes in Chinese-Type Paste as Affected by Prefrying Methods

The aim of this study was to determine the textural and sensory properties of herring (Clupea harengus) cubes prefried by deep frying (DF), mild frying (MF), and vacuum frying (VF) in Chinese-type pastes stored for 25 days at 13–15°C. Three groups of fish cubes in every Chinese-type paste were compared for texture, physical, and sensory properties by carrying out texture profile analysis (TPA), moisture content, color, and sensory analyses; and two types of Chinese-type pastes were investigated, oily Paste (A) and light Paste (B). The results showed that L* of fish cubes decreased significantly (p < 0.05), and a* and b* increased significantly (p < 0.05) in two kinds of Chinese-type pastes. Fish cubes prefried by DF and MF had higher sensory scores in Chinese-type Paste A, while those prefried by DF and VF had higher sensory scores in Chinese-type Paste B.     

Effect of Genetic Algorithm Optimized Solar Tunnel Dryer on the Quality Attributes of Thin-Layer Dried Fish

ABSTRACT

Studies were undertaken to establish the performance of a genetic algorithm-optimized solar tunnel dryer in drying of fish by comparing quality attributes of fish dried in the optimized solar tunnel dryer with that dried in a nonoptimized solar tunnel dryer and in open sun. A two-way analysis of variance revealed a highly significant difference between moisture ratios for the fish dried under the optimized solar tunnel dryer and the other methods (F = 53.59, F_crit,1% = 4.09). In addition, thiobarbituric acid reactive substances showed that fish dried in the optimized dryer did not develop rancidity (2.30 µg MA/kg), that dried in nonoptimized dryer approached rancid values (5.3 µg MA/kg), while open sun dried fish was slightly rancid (7.95–8.45 µg MA/kg). Further, based on total volatile base nitrogen, fish under the three drying treatments did not develop significant putrefaction. Furthermore, it took 15, 22, and 28 h to dry fish to equilibrium moisture content of 0.12 kg/kg (dry basis), for the optimized and nonoptimized solar tunnel dryers and for the open sun drying, respectively. Thus, the optimized solar tunnel dryer is superior to both nonoptimized solar tunnel dryer and open sun drying in the drying of fish.     

Microwave irradiation and pelleting method affected feed chemical composition and growth performance and feed utilization of sex‐reversed Nile tilapia,Oreochromis niloticus (L.)

Microwave processing and pelleting methods were assessed to improve aquafeed quality for sex‐reversed Nile tilapia. The 2 × 3 experimental feeds were prepared with and without microwave irradiation of ingredients prior to pelleting with either a meat mincer, extruder or steam conditioner followed by a meat mincer. Five feedstuff ingredients, including fish meal, meat and bone meal, soybean meal, broken rice and rice bran, were irradiated separately at optimal times, according to the third‐order polynomial regression analysis between in vitro digestibility and microwave irradiation times (r = 0.681–0.942, P < 0.001, n = 42). The prepared feeds were studied for chemical compositions and responses in fish growth performance and feed utilization efficiency. The fish (1.57 ± 0.01 g initial weight) were fed ad libitum for 4 months. All proximate chemical compositions of experimental feeds, except protein, were influenced by microwave processing, pelleting methods or their interaction (P < 0.05). There were no significant effects from either parameter on water quality during the fish trial. Fish fed steamed microwave‐irradiated feed, mechanically pelleted with a meat mincer, showed the highest growth performance (weight gain 18.91 ± 0.73 g and specific growth rate 2.15 ± 0.26% day^?1) and feed utilization efficiency (feed conversion ratio 1.31 ± 0.05 g feed g gain^?1 and protein efficiency ratio 2.27 ± 0.08 g gain g protein^?1) compared with the other dietary groups. These findings indicate that microwave irradiation of feed ingredients prior to steam conditioning followed by mincing can improve aquafeed production quality.     

Hormonal sex reversal of tilapias: implications of hormone treatment application in closed water systems

The phenomenon of incidental sex reversal was observed in experiments originally designed to determine the importance of feeding duration and feed quality in the optimization of masculinization and feminization treatments of Oreochromis niloticus (L.) fry by oral application of hormones. Four separate experiments were conducted: (1) masculinization and (2) feminization using three feeding durations and (3) masculinization and (4) feminization using three alternative feed mixtures. Masculinization experiments incorporating 17 α-methyltestosterone (MT) into the feed at 40 mg kg^?1 were applied to putative monosex male progeny whilst feminization treatments were applied to putative all female fry using diethylstilboestrol (DES) at 1000 mg kg^?1. Treatments were applied outdoors in small cages suspended in 900-l circular concrete tanks with a flow through rate of 1-l min^?1. Replicate cages for all treatments and the controls in each experiment were reared together in the same tank. Only the first experiment produced significant differences in sex ratio, with the control treatment producing a slightly lower proportion of males than the three MT treatments at different durations. The most significant finding was that in all experiments the sex ratio of the control differed significantly from expectations and in all but experiment 1, did not differ from those of the treated fish in which sex reversal had clearly been effected. It appears likely that incidental sex reversal occurred in the control fish as a result of the accumulation of active metabolites from the treated fish and/or leachates from uneaten food given to fish in the same water body. The results are discussed in the context of improving the efficiency and safety of hormonal sex reversal treatments.     

Modeling the Inclusion of Fish Powder and Fish Oil into Extruded Snacks by Response Surface Methodology

ABSTRACT

Extrusion cooking plays an important role in the production of puffed snacks, which enjoy wide acceptance all over the world and are potential vehicles for increasing the consumption of n-3 fatty acids. Response surface methodology (RSM) with central composite design was adopted to investigate the effects of four independent variables (fish powder, fish oil, moisture, and screw speed) at five levels on expansion ratio, breaking strength index, hardness, color, and thiobarbituric acid reactive substances (TBARS). A second order polynomial model was used to study the main, interactive, and quadratic effects of the independent variables and to explain the relationship between the responses and independent variables. Moisture was found to be the most significant factor (p < 0.001) influencing expansion ratio, breaking strength index, and color. Inclusion of fish powder and fish oil were found to be negatively associated with the expansion characteristics, resulting in decreased lipid oxidation due to less exposed surface area of the extrudates to air. Further, the absence of linear effect of fish powder and fish oil on TBARS demonstrated the possibility to incorporate higher levels of these ingredients to produce oxidatively stable extruded snacks rich in fish proteins.     

The nutritional properties of co-dried fish silage in rainbow trout (Salmo gairdneri) dry diets

Feed ingredients containing fish silage and liquefied fish made from ground, whole Pacific whiting and co-dried in a vacuum dryer with mixtures of soybean meal and feather meal to facilitate drying were prepared. An additional batch of fish silage was co-dried with the other dry ingredients in the diet formulation that was used, Abernathy diet S8-1. Fish meal, made by vacuum drying Pacific whiting, was used in the control diet. Co-dried fish meal was made by co-drying Pacific whiting with a soybean meal-feather meal mixture. Fish meal was entirely replaced by the co-dried products in the experimental diets, which were fed to rainbow trout (Salmo gairdneri) for 32 weeks. The best growth and food conversion values were obtained by feeding the fish meal control diet or the diet in which the fish meal was replaced with co-dried liquefied fish. No significant differences in final weights were found between trout fed diets containing co-dried fish meal or co-dried fish silage (fish products were 25% of the diet), but these fish were significantly smaller than fish fed the fish meal control or the co-dried liquefied fish diets. Reducing the fish silage to 12.5% or increasing it to 50% further reduced weight gains in the trout. Food conversion values, protein efficiency ratios, and net protein utilization values generally followed the same trends between diets as did the final weight values. Apparent digestibility coefficients for the co-dried products were lower than for the fish meal, possibly because they contained soybean meal-feather meal mixtures. Organoleptic properties of the fish were not affected by diet.     

Growth, feed utilization and carcass composition of catfish Clarias batrachus (Linn.) fingerlings fed on dried fish and chicken viscera incorporated diets

A 30‐day feeding trial was conducted to evaluate dried fish and chicken viscera, and a combination of oil cakes as complete substitutes for fish meal in the diet of catfsh Clarias batrachus (Linn.) fingerlings. Triplicate groups of fingerlings with a mean initial body weight of 2.0 g were each fed four isonitrogenous diets at 4% of wet body weight. Performance of the diets was judged on the basis of feed acceptability, body weight gain, feed conversion ratio and protein efficiency ratio. A significant increase (P < 0.05) in body weight gain, protein efficiency ratio and a decreased feed conversion ratio (P < 0.05) was observed in fish fed on fish meal, followed by fish viscera, chicken viscera and only plant protein incorporated diets. Although inferior to fish meal and dried fish viscera, growth and feed utilization responses of fingerlings fed on dried chicken viscera and plant protein diets were similar. The fish accumulated a significantly greater (P < 0.05) amount of fat (18.3%) in the body carcass when fish viscera was incorporated in the diet. The study revealed that satisfactory growth and feed utilization responses could be achieved through replacement of fish meal by dried fish and chicken viscera in the diet of catfish fingerlings.     

Preparation and Storage Characteristics of Ribbon Fish Laminates

Abstract

A process to prepare dehydrated laminates of ribbon fish is reported. Pieces of eviscerated and beheaded fish were pressed under a screw press and the laminates obtained were subjected to air drying at 55°C for 14 hr. The product was golden brown in color, and had 18.4% moisture, 22% rehydration capacity, and pepsin and trypsin digestibilities of 51 and 62%, respectively. Oxidation of lipids during aerobic storage of the product at ambient temperature could be controlled by vacuum packaging. Sensory evaluation of the productfried in vegetable oil after Serobic storing at ambient temperature for 100 days suggested its acceptability. The process has potential for value addition of ribbon fish.     

Substitution of fish meal with raw or treated cowpea (Vigna unguiculata L Walp,IT86‐D719) meal in diets for Nile tilapia (Oreochromis niloticus L.) fry

Two feeding experiments were carried out to evaluate the effect of partial substitution of fish meal (FM) with raw or heat‐treated cowpea Vigna unguiculata L. Walp var. IT86‐D719 seeds on growth performance, digestibility and pancreas tissue in Nile tilapia (Oreochromis niloticus L.) fry. Experiment 1 involved six isonitrogenous and isocaloric diets: four containing different concentrations of raw, whole cowpea meal (protein basis), a positive control with FM as sole protein source and a negative with cowpea meal as sole protein source. Substitution at up to 200 g kg^?1 had no significant effect on production parameters, although growth was negatively affected in the negative control because of seed antinutritional factor content. Experiment 2 evaluated the effect of heat treatment (oven drying at 48 °C; hot air drying at 70 °C; or autoclaving at 119 °C) and/or seed dehulling using diets containing 200 g kg^?1 cowpea meal presoaked in water. Only autoclaving eliminated trypsin inhibitor and lectin contents, independent of dehulling. Histological analysis indicated no histological changes in pancreas tissue. Raw or treated cowpea meal can replace FM in tilapia fingerling diets at up to 200 g kg^?1 protein content without significantly affecting productive parameters or pancreas tissue.     

干燥方法及保存条件对小球藻粉脂肪酸含量和种类组成的影响

研究了低温烘干、真空冻干和微波干燥3种干燥方式对蛋白核小球藻粗脂肪、脂肪酸含量和种类组成的影响及不同保存条件下脂肪酸的变化规律。试验结果表明,低温烘干藻粉的粗脂肪含量明显低于真空冻干藻粉和微波干燥藻粉。3种干燥方式对小球藻脂肪酸含量无显著影响,但藻粉颜色明显不同。藻粉脂肪酸含量与鲜藻之间无显著差异。在小球藻粉保存过程中,脂肪酸种类组成保持不变。藻粉在常温(14.5～18.5℃)下保存半年、4℃下保存1年时,多不饱和脂肪酸含量显著减少,饱和脂肪酸和单不饱和脂肪酸含量显著增加。在-24℃下保存1年时,各脂肪酸含量无明显变化。     

大型海藻干燥技术研究进展

干燥是海藻储存、加工、生产的重要方法之一,不同的干燥方式对海藻脱水效率、能耗和品质影响很大。本文对藻类传统干燥和新型干燥技术的特点、研究及应用现状进行了分析。研究表明,太阳能干燥技术能够充分做到干燥过程中绿色、环保,与空气热泵构成组合干燥模式,可解决太阳能不连续的问题;过热蒸汽干燥效率高、能耗低,藻类干燥后复水性好;真空冷冻干燥产品品质好,能最大限度保持藻类的营养和功能性成分;远红外加热技术对海带进行干燥,与同风速的热风干燥相比,可显著缩短干燥时间,降低能耗;微波真空干燥技术干燥江蓠,在保持品质的基础上干燥时间较热风干燥减少70%。本文同时对藻类干燥技术与设备存在的问题进行了总结,对国内藻类干燥技术及装备的发展趋势进行了展望并提出了措施与建议。     

Effect of drying on the viability of the probiotic bacterium Lactobacillus plantarum Lab9 (CPQBA 144‐09 DRM 03) impregnated in the feed for tilapia (Oreochromis sp.)

Drying experiments were conducted at different temperatures and air flux velocities to determine the proper drying conditions for reducing moisture in commercial fish feed impregnated with probiotic lactic acid bacteria and to assess the effect on bacteria viability over time. At temperatures of 45°C, the drying time was shorter, without the air flux velocity under study having a relevant influence. The drying conditions influenced the viability of the bacteria in the feed; the least loss of viability was obtained with a velocity of 0.8 m s^?1 and a temperature of 45°C during 15 min. Using these drying conditions, 5 kg of feed was dried and stored for a month at temperature of 26°C and relative humidity of 75%. The viability of the bacteria and the moisture of the feed were measured every 3 days during the storage period. Loss of viability followed first order kinetics, with a constant k of 0.112 days^?1. Thus, the viability of the bacteria in the feed is less than 10⁶ CFU g^?1 after 43 days.     

Replacing fish meal with chicken offal silage in commercial Oreochromis niloticus (L.) feed

Four isocaloric isonitrogenous rations containing various levels (0,10, 15 and 20%) of chicken offal silage as a replacement for fish meal were fed to three replicate groups of Oreochromis niloticus (L.) fingerlings with a mean initial weight of 10.8g. Ten fish per tank were tested for 5 weeks in 40-1 aquaria. The aquaria were put together in a flow-through system utilizing underground water (24 ± 3°C). Weight gain, feed conversion, protein efficiency ratio and proximate body composition did not vary significantly between treatments. These results indicate that, on an isocaloric/ isonitrogenous basis, chicken offal silage can make up as much as 20% of O. niloticus commercial feed as a replacement for fish meal without any effect on growth or proximate body composition under the experimental conditions.     

Evaluation of mosquito fish Gambusia holbrooki (Girard) as a partial and complete pellet replacement for juvenile barramundi Lates calcarifer (Bloch)

Barramundi (Lates calcarifer, Bloch) fed live mosquito fish (Gambusia holbrooki, Girard) exhibited faster growth and a better food conversion ratio (on a dry‐weight basis) than those fed an iso‐calorific ration of commercial barramundi pellets and a 50:50 ration of mosquito fish and pellets. The improved performance of barramundi fed mosquito fish was attributed to their higher protein content, higher protein to energy ratio and lower carbohydrate content. The essential amino acid indices and fatty acid profiles of the two diets were similar, suggesting that imbalances or deficiencies in these nutrients were not the limiting factor to the slower growth of barramundi fed on pellets. The use of mosquito fish as barramundi food offers a potential use of this noxious species and may allow barramundi to be cultured without the use of conventional fish meal.     

Water‐soluble protein level in fishmeal affects extrusion behaviour,phase transitions and physical quality of feed

The aim of this research was to investigate the effect of water‐soluble protein (WSP) as a plasticizer in the fish feed extrusion process and the impact on physical pellet quality. A three‐factor central composite design was used to study the influence of the variables WSP in the feed mix, and steam and water addition in the extruder. Regression models with r² in the range of 0.862–0.976 (P < 0.001) were established for specific mechanical energy (SME), pellet hardness, cutting strength, sectional expansion index, length, bulk density, oil adsorption capacity and extrudate flow‐starting temperature (T_f). Addition of WSP had a positive effect on SME and improved the physical pellet quality, while moisture had the opposite effect. Expansion parameters showed a complex relationship and were influenced by all the studied process variables. Increase in WSP and moisture content had a comparable effect on T_f reduction. This opens up the possibility to obtain a satisfactory ‘cook’ at reduced moisture level with a potential for significant reduction of the energy consumption during drying of the extrudate. Overall conclusion from the experiment is that WSP can be used as a processing aid for the fish feed industry, serving multiple purposes as nutrient, plasticizer and binder in extruded fish feed.     

Effects of Preservation Methods On Geosmin Content and Off-Flavor in Nile Tilapia (Oreochromis niloticus)

Abstract

In this study, the masking or reduction of off-flavor in tilapia due to various preservation methods such as salting, drying, frying, smoking, microwave heating, marinating and fermentation with carbohydrate mixture (som fak preparation) was investigated by subjecting the processed tilapia to sensory evaluation and analyzing the concentrations of geosmin (1,10-trans -dimethyl-trans -9-decaol) in the processed samples. Dry salting or brining muddy-flavored fish and then drying either by hot air at 50°C or sun-drying resulted to only a slight reduction in the geosmin content of the product. Deep-frying reduced the muddy flavor intensity and geosmin content in salted-dried tilapia. Pretreatment of tilapia fillets with acidified brine before smoking reduced geosmin content and masked the muddy flavor in the smoked product. Microwave cooking of fresh muddy-flavored tilapia showed no effect on its geosmin content nor its off-flavor. Marinating tilapia in acetic acid solution resulted in decreased muddy flavor, and longer marinating period led to lower geosmin content in the product. The geosmin content of som fak made from muddy-flavor and non-muddy-flavor tilapia differed significantly, although sensory evaluation yielded no significant differences between the two types of som fak, and the taste panelists preferred the product fermented for 3 days.     

Evaluation of full-fat and defatted maggot meals in the feeding of clariid catfish Clarias gariepinus fingerlings

The nutritional implication of processed maggot meals, hydrolysed, defatted, full‐fat, sun‐dried and oven‐dried, in the diets of Clarias gariepinus fingerlings were evaluated. The nutrient density, proximate composition, gross energy and mineral constituents of the maggot meals were determined. Five isonitrogenous and isocaloric diets were formulated to provide 40% crude protein in which fish meal in the reference diet was completely replaced by any of the following processed maggot meals: oven‐dried full‐fat (ODM), sun‐dried full‐fat (SDM), defatted oven‐dried (DODM) and defatted sun‐dried (DSDM) maggot meals respectively. Fish were fed ad libitum in triplicate treatments for 56 days in glass tanks. Biological evaluations of the fish were based on growth performance and nutrient utilization indices. The result of the nutrient composition analysis showed that processing methods of defattening and drying influenced the nutrient density of maggot meal, with crude protein content ranging between 43.30% and 46.70% for full‐fat sun‐dried and hydrolysed/defatted oven‐dried maggot meals respectively. The result showed that growth performance and nutrient utilization of fish fed DODM and DSDM dietary inclusions were not significantly different and similar to fish fed the fish meal‐based diet. However, fish fed the diet containing SDM exhibited lower daily weight gain, protein efficiency ratio and specific growth. Generally, fish performed better when fed diets containing defatted maggot meals than full‐fat maggot meal, and compared favourably with fish fed the fish meal‐based diet.     

Simple field methods for monitoring stress and general condition of fish

While physiological stress in fish can be assessed by several laboratory-based methods, many of those methods use very sensitive and expensive instruments, which make them impracticable under field conditions. The objective of this study was to determine the feasibility of detecting stressed states in fish, under Held conditions, using simple but reliable methods. The first set of experiments were conducted in the laboratory, where a standard handling stressor was applied to juvenile coho salmon, Oncorhynchus kisutch (Walbaum). Results of blood samples analysed by both laboratory-based and portable methods (e.g. glucometers for diabetic patients) were in good agreement. The second set of experiments focused on field-testing the most promising methods based on the laboratatory tests. Production lots of Atlantic salmon. Salmo salar L., at commercial fish farms were sampled to assess stress and health status with the selected field techniques, from the swim-up to smolting stages. The measured variables included: blood glucose, protein, haemoglobin concentrations: haematocrit: erythrocyte and lymphocyte numbers: and an autopsy-based health profile, which involved the internal and external examination of the body for texture and colour. In addition to establishing resting, or normal, values for each variable under field conditions, blood glucose levels were observed to increase significantly at 4 h after a stressful event (e.g. grading, handling) using these field methods. Some of these field techniques were found to be reliable indicators of stress in fish and have potential for use in aquaculture facilities and field monitoring programmes.     

Growth and health performance of African catfish Clarias gariepinus (Burchell 1822) juvenile fed with graded levels of biofloc meal

The objective of the study was to evaluate the utilization of biofloc meal as a feed ingredient in enhancing the growth and health status of African catfish (Clarias gariepinus) juvenile. The study consisted of two experiments, that is digestibility and growth experiments. The digestibility of two biofloc meals produced with two different carbon sources, that is tapioca and molasses, were assessed in the digestibility experiment. Whereas the effect of four dietary treatments with different levels of biofloc meal, that is 0%, 5%, 10% and 20%, on the fish growth performance, feed utilization, immuno‐haematological response, antioxidant status and robustness against environmental stress were evaluated in the growth experiment. The results showed that the digestibility of dry matter, protein, lipid and phosphorus of biofloc grown using molasses as the carbon source were remarkably higher than that grown using tapioca (p < 0.05). The inclusion of biofloc meal in the diets at 10% and 20% resulted in higher feed intake, fish growth and final biomass and protein efficiency ratio, and lower feed conversion ratio (p < 0.05). Furthermore, the red blood cells counts, phagocytic, lysozyme activities and antioxidative capacity were significantly enhanced in the fish provided with diet containing 20% biofloc meal (p < 0.05).The fish survival following salinity stress test was higher in the treatments with biofloc meal at 10% and 20% inclusion levels. In conclusion, dietary inclusion of biofloc meal could improve the growth performance and health status of African catfish juvenile and an inclusion level of 20% could be recommended.