A comprehensive review on freshness of fish and assessment: Analytical methods and recent innovations

Highlights

• Review article appraises the biochemical and microbiological changes and major volatiles formation in stored fish.

• It explores specifically about the protein and lipid breakdown in the muscle.

• Included chemical, microbiological and physical indicators of fish freshness.

• Enriched with recent innovations and developments on freshness indicators and assessment.

• It has also made systematic and in-depth information of fish freshness in tabular form.

Abstract

Fish, a highly nutritious, containing a good amount of protein and fatty acids, has TMA and TVB-N present as major factors responsible for quality deterioration during storage and maintaining of fish freshness. Freshness is one of the most important parameters in the fish market. There are many methods of estimating fish freshness, out of which some are very costly while others are not user-friendly. However, with more technological innovations, there have been efforts to make a more reliable method of calculating and analyzing freshness. Parameters chosen for assessing the freshness are sensory, physical, chemical and microbiological including the recent trends such as SDS-PAGE, fast protein liquid chromatography, hyper Spectral Imaging Technique, etc. focused on reducing time, destruction and labor. Traditional and recent methods of evaluation of freshness along with their comparison based on several parameters are needed to link them and making it convenient for upcoming researchers to have a detailed study for having a universal indicator for assessing the freshness of fish. Information in the present article has all the methods of assessing the fish freshness been discussed in detail. There has also been focus on bringing the readers knowledge about the comprehensive information related to recent developments. The recommended limit for different indicators signifies the time period for which the particular fish can be stored and it depends upon several factors like species, surrounding environment and enzymatic and non-enzymatic actions. Based on these demands, this paper is uniquely worked upon to review the different literature which brought all the discussions from the past including the recent innovations in assessing the freshness of different fishes with the help of various indicators as well as a complete study of spoilage and toxicity mechanism leading to deterioration in quality, making it easy for the reader and researchers to have quick glance over the trends and innovations.

Introduction

The demand for fish has been ever-growing due to the increasing human population and more research in fisheries which has increased the demand over the last few decades across the world. The recent preservation techniques have made it possible to make the same quality of processed fishes reach across different parts of the world. In 2016, global fish production was 171 million tonnes, in which 47% of total inclusion is of aquaculture and the other 53 percent comes under non-food uses (and includes fishmeal and fish oil) (FAO, 2018). Since the 1980 s, the production of captured fish has remained constant; the continued accelerated growth in the supply of fish for human consumption has only been possible due to aquaculture. The human consumption increased from 130 to 151 million tonnes from 2011 to 2016 while non-food uses reduced from 24 to 19.7 million tonnes. While the total capture leads to 92.7 million tonnes including both 11.4 MT from inland and 81.2 MT from marine water, at the same time the aquaculture production leads to 80 MT of fish with 52 MT from inland and 28 MT from the marine population (FAO, 2018). A total of 59.6 million fish farmers exist in the globe out of which 85 percent are supported over capturing and aquaculture belong to Asia. The direct consumption of fish leads to 88% that is 151 million tonnes while only 12% was processed for non-food and aquaculture related requirements (FAO, 2018).

Fish is highly nutritive, being full of protein, vitamins, and minerals which are required by our body for good health and well being. Fish has been mainly classified into mainly 3 categories: (1) oily fish, (2) white fish and (3) shellfish (Naylor et al., 2000). Oily fish contains a good amount of vitamins A, D and E. Being rich in omega-3 fatty acids, it keeps the brain healthy, is beneficial for the eye and important for the nerve development in babies. Their consumption also keeps the heart healthy and there are enough proofs to assure that its consumption reduces the risk of cancer and arthritis (Lees, 1990). Therefore, such a large population today directly or indirectly depends on fish either as a nutritious diet or as a source of income. But the biggest challenge in fulfilling the needs of all the population is the perishability of fish. Fish is highly perishable and the production of various metabolites responsible for its spoilage starts right after it is harvested. Hence, there has been so much focus on estimating the freshness and behavior of fishes in different conditions which are due to the increasing demand and awareness of fish products both from the nutritional and informational factors. Apart from this, the fish industry is a prime economic source for trade (international and domestic) in the coastal states and districts. Human consumption of fish and fish related products around the world is about 128 million tonnes, and this consumption for a single person is 18.4 kg of fish products per year (Durand & Seminario, 2009). All the fish products make a proportion of 15% of the animal protein intake for 4.3 billion people as per the report of the 30th conference of Fisheries Commission of Food and Agricultural Organization (FAO, 2012). The methods of evaluating fish freshness have been dated back since the mid-20th century and the advances in the last 3 decades have been the most rapid and innovative ones. But some of these techniques are easy and simple to use but at the same time, time-consuming while on the other hand, many techniques take less time to show the results but are expensive and complex methods (Prabhakar, Srivastav, & Pathak, 2019).

New and innovative technologies have enhanced both the product qualities and maintain the same characteristics throughout the period from when it was harvested to the point the consumer will intake it as a meal. There have been regulations according to many countries to establish the principles which can control and certify the quality warranty relating to fish products as a whole. Codex is the international body which makes standards for fish commodities and has constituted various committees to look after these standards. For example, under commodity committees, comes fish and fish products (Norway), fats and oils (United Kingdom), meat and meat products (West Germany). Similarly, in India, the Food Safety Authority of India (FSSAI) looks after the laws and regulations regarding the production and sale of different fish and related products. Physical, chemical, microbiological and biochemical changes occurring post-mortem in fishes, resulting in a progressive loss of food characteristics in terms of taste and quality. Storage time and temperature are key factors for the final quality of the product. The rate of spoilage however also depends on many other factors such as kind of fish species, the sanitary conditions on board, and the amount of food in the guts (Ghaly, Dave, Budge, & Brooks, 2010). When it comes to consumers’ point of view, the taste is, of course, the most important aspect which is directly proportional to the fish freshness and hence the most required property. How taste is related to the freshness of fish needs to be understood by the fact that with days passing after the freshly harvested fish, the volatile products responding to the smell and the change in texture while chewing leads to less preference by most of the people.

All the methods use a common strategy, the base being the calculation of total volatile basic nitrogen (TVB-N) and trimethylamine (TMA) over different periods of storage directly or indirectly to assess the freshness of fish (Table 1). Several methods have been thus developed in the recent past to determine the fish freshness. The sensory evaluation uses sight, smell, odor, tactile, etc. to measure the freshness of fishes. A trained panel can evaluate all these sensory attributes quite well and each qualitative description is converted in a numeric score which helps to differentiate the samples as well as information about the sample. However, the trained panels are generally expensive and not always available at different steps of the fishery chain. Hence to satisfy the high-quality based inspection and determination of fish freshness, the food industry the initial phase of development of instruments was made in vision to replace it exactly with human senses to detect the freshness. Some of the examples are texture analyzer for firmness, electronic nose (EN) for odor, and colorimeter and skin image coherence for skin appearance (Table 3). Dalgaard (2000) developed a microbial inspection to know the remaining shelf life by calculating the amount of TMAO consumed by different species of bacteria. The total viable count (TVC) is calculated in the fishery products and thus the freshness is determined (Table 1, Table 2, Table 3). During fish storage, the increase in TMA-N has been widely correlated with a decrease in TMAO concentration. Recent developments after 2009 have included EN technique, hyperspectral imaging technique, and fast protein liquid chromatography to assess autolytic and microbiological changes in the fish samples which proved to be non-destructive, less time consuming, but need highly expert and trained people for performing the experiments successfully (Table 2) (Cheng et al., 2013, Cheng et al., 2015).

The chemical inspection has involved a wide area of research in which different scientists have studied the chemical changes on different fish species and using a range of instrumental methods. Hassoun and Karoui (2017) held that the basis for chemical inspection has been the determination of K value, Peroxide value, TVB value, Oxidation Reduction Potential, P ratio, K value, etc. Spectral imaging and NMR spectroscopy have been recent advances being the non-destructive, less time-consuming, non-contact and reliable technique. But the major problem related to this is that these techniques do not apply to all varieties of fish and there needs more research after which the same parameter can be applied to all kinds of fish related products. Moisture measurement, volatile compounds measurement, protein changes in post-mortem storage, lipid oxidation monitoring, ATP decomposition, K value indicator are important parameters of measuring chemical inspection for fish freshness.

Physical properties measurements include color measurement and texture measurement specifically while the shape, size, volume and weight also play a major role in determining the freshness (Olafsdottir et al., 2004). Color and textural changes have a direct impact on the freshness of fish. Initially, the only colorimeter was used to detect the color in fish, but now we have many novel methods for investigating the same (Table 3). But these novel methods require in-depth research for more samples and varieties of fishes as compared to other methods of inspection. The connection of the research with mathematical modeling has made it possible to have a valid and authentic proof for every experiment the scientists have conducted. In one or more ways finally, all the models are interconnected being able to finally detect fish freshness and at the same time, the approaches of each technique are quite unique and different from each other. Hence, there has been much research and development regarding the determination of freshness of fish but the world today still needs a much faster and simple to use universal indicator which would be applicable to all the fishes and the research regarding this is already going and it is assumed that researchers will be successful to achieve this target till next decade.