Developing Minced Fish Products of Improved Eating Quality: An Interplay of Instrumental and Sensory Texture

Abstract

This treatise attempts to combine effectively data from instrumental and sensory texture, thus overcoming the empiricism pervading the development of processed fish products. Traditional fish burgers or sausages are made mostly with added starch but fail to offer a new marketing position that satisfies consumer's expectations of a tasty meal. However, the eating quality of minced fish products can be improved by including in the formulation relatively small amounts of proteins and non-starch hydrocolloids, thus taking advantage of their multifaceted functionality as texture modifiers. Such product formulation leads to the identification of distinctive upper and lower bounds of the attributes of instrumental texture in relation to increasing sensory acceptability. This can be further manipulated via a strong correlation between instrumental and sensory attributes of texture engineered by increasing the concentration of a single ingredient in the formulation. Within this extended spectrum of valid implementation of the quantitative descriptive analysis (QDA), affective testing can pinpoint a particular preparation of optimum overall consumer acceptability.

Keywords:

• Fish burgers
• Fish sausages
• Instrumental texture
• Sensory texture
• Quantitative descriptive analysis

INTRODUCTION

Background to the Development of Minced Fish Products

The continuous development of processed food formulations constitutes a large part in the advance of the welfare of a country and contributes many benefits to the life of the average consumer. This is more apparent than ever in the case of fish products, with the increasing consumer awareness of the positive health implications of a diet rich in fish guaranteeing high demand for marketable embodiments.[1] Furthermore, industrialists strive to develop some of these formulations with inexpensive fish resources in order to improve profit margins. Such an undertaking requires innovation and fundamental understanding of the processes determining texture in order to ensure a commercial outcome with increasing likelihood of consumer acceptability.[2]

Early examples in the development of processed fish products were based exclusively on minced or filleted fish with some addition of preservatives, e.g., polyphosphates, which reduce drip loss especially in products made from thawed frozen fish. Condiments can be added to taste according to market requirements. It is well known among the artisans in the field that fish muscle protein does not possess enough functionality to hold together a cohesive processed product.[3] As the industry expanded, corn flour or corn starch was introduced to enhance the structure and cohesion of products made increasingly from a mixture of prime and inferior cuts of minced fish.[4,5] Still, those were not satisfactory and a plethora of formulations were thought up to improve the texture of the final product, a case in point of which is given below.

1.	Several varieties of starch (wheat, rice, and barley) were used together in various fish products as the main or supporting dish in the presence of vegetables selected from greens, aubergines and salads, and/or simple condiments from vegetable oil, olive oil, and soy sauce.[6,7]
2.	Being aware of the unacceptably soft consistency of the fish muscle, researchers attempted to firm up processed embodiments by utilising cross-linking reactions. The outcome was a bonding gel layer in the presence of a reducing agent and activated transglutaminase that induce aggregation of the protein fibrinogen.[8] Composite fish (or even meat) products of improved functionality can be obtained in this way from fish, crustaceans, snails, frog legs, etc.
3.	A particular case of the above undertaking was the making of a frozen ready-to-cook fish patty, which was shaped and frozen in a desired shape and could incorporate seasoning materials, water, onions and a grain product. Microscopy images demonstrated that preparations could comprise a matrix of finely minced fish meat supporting a phase of chopped fish meat homogenously dispersed in the matrix thus adding to the textural manipulation of the dish.[9]
4.	And yet, it was clear that incorporation of starch in the formulation was not sufficient to design textures with maximum likelihood of acceptance by the consumer. Gradually, non-starchy hydrocolloid technology was brought in to reach such a target. The gelling ability of mannan hydrate or glucomannan hydrate was utilised in industrial formulations which comprised non-salt minced fish meat.[10,11] Furthermore, a patented invention disclosed a process for improving fish meat or minced fish meat quality by treating the meat with an aqueous solution of a calcium salt, and dehydrating to a moisture content of 70 to 90%. This was followed by adding 0.1 to 10%, in terms of the dry matter of the fish meat, of one or more materials selected from plasma protein, serum protein, albumen, and cow's milk.[12,13]
5.	Finally, the multifaceted functionality of pectin polysaccharide with a degree of esterification between 30 and 80% was exploited in a process for producing a ready-to-cook protein base of fish muscle flesh. Texturisation of the product was further regulated by various protein-rich edible materials, fats and salts of polyvalent cations.[14–16]

When conventional fish products, such as those referred to in the aforementioned examples (i.e., based on minced/filleted fish, and mixtures of fish with corn flour/starch or glucomannan/pectin polysaccharides) are assessed by taste panels, they are often found not to yield desirable eating quality. Evidently, the processes and products referred to in the aforementioned industrial specifications or published literature lack the necessary technical and technological reliability for achieving optimum mouthfeel and textural desirability. Novelty claims made within the patented domain are not easily substantiated due to the lack of rigorous scientific characterisation of these inventions.[17]

The aim of this short review is to negotiate the development of processed fish products based on hydrocolloid technology. Ingredient functionality is related directly to proper physicochemical characterization, thus setting up a platform for correlation with the quantitative description and hedonic profile of the products via trained or untrained sensory panels.

PREPARATION OF INDUSTRIAL FORMULATIONS OF FISH PRODUCTS USING HYDROCOLLOID TECHNOLOGY

The concise nature of this review requires that it focuses on fish burgers or sausages made from raw fish fillet or mince but the fundamental approach adopted presently can be considered as a working protocol for the successful development of similar products (nuggets, fingers, pate, etc). The proportion of fish muscle among the components of the burger/sausage formulation depends on the market requirement and fish species thus varying, for example, from 70% tuna and 50% shark meat to 30% whale red meat.[18,19] A critical requirement for the financial viability of such an undertaking is to develop a formulation based as much as possible on commercially underutilized fish thus gaining an advantage over market competitors.

For the sake of brevity, we opted to relate in here work carried out on spotted croaker, Protonibea diacantha, belonging to the family Sciaenidae (Croakers, Drums and Meagres).[20] The spotted croaker has a wide distribution and is found from Japan and China south to Queensland and west along the southern Asian continent to the Arabian Sea. Above all, however, this is a rather inexpensive resource (about 0.8 US $ per kilo of raw fish in South East Asia), as compared to the highly sought after kingfish, tuna, emperor, etc, which can fetch five times as much in the local fish market.

Besides fish meat, which constitutes most of the formulation, an artisan with expert knowledge of hydrocolloid structure-function relationships can utilise those to demonstrate quality control of the end product, as follows.

1.	Corn/wheat/rice starch remain part of the hydrocolloid mix to provide a basic matrix of structure thus preventing loss of volume upon drying during processing or cooking.[21]
2.	Commercial milk concentrate containing lactose and milkfat, or soy isolate impart a rich mouthfeel (creaminess) to the palate, and constitute a good source of required minerals in the diet (e.g., calcium).[22,23]
3.	The melt-in-the-mouth property and clarity of porcine / bovine gelatin and citrus peel pectin should be considered in mixture with the aforementioned hydrocolloids, with the structuring ability of pectin being further manipulated based on the degree of esterification and amidation.[24,25]
4.	Advanced hydrocolloid technology can be implemented with additions of alginate (plus calcium ions), κ- or ι-carrageenan (plus potassium ions) and deacylated gellan gum (plus sodium ions),[26,27] but this requires substantial investment in the R&D unit of the company to master the effects of phase-separated topology of composite gels.[28,29]
5.	Finally, dried apples, dates and apricots, frozen garden peas, diced carrots, corn kernels, cut green beans, garlic powder, oriental spices, black pepper, monosodium glutamate (MSG), sucrose, polyphosphate, table salt, calcium chloride / lactate, potassium chloride, and ice water may be included in the formulation to achieve the desired flavour release and optimize the mouthfeel.[30]

A general protocol of preparing a given product once ingredients in the formulation are finalised is as follows:[31] Fish is headed, gutted, and visceral mass removed. Gutted fish is filleted mechanically or with knives. Fish fillets are first chilled at 2°C usually for 2–3 hours, and then frozen for up to four weeks depending on the constraints of the industrial process. One of the outcomes of this treatment is to harden the flesh, which improves the structural properties of fish meat in the final product.[32] Following storage, fillets are minced using crushing and fine cutting with various choppers to yield homogenized mince. Preparations are made by blending appropriate amounts of fish meat with starch, non-starchy hydrocolloids, vegetables, dry fruit leathers, condiments, sucrose, etc.

If gelatin is to be used, dissolution by heating up to 70°C and stirring for 20 to 30 min are required.[33] Low methoxy pectin, alginate, and carrageenans should be dissolved at 90°C using stirring for 30 min followed by addition of calcium chloride/lactate (e.g., at 40% stoichiometric equivalent) and trisodium citrate sequestrant for the pectin or alginate polysaccharides, and potassium chloride (10 to 100 mM) for the carrageenans.[34]

The homogenous mixture is stuffed in manually/automatically operated machines for pressing thus producing firm and free from air burgers of variable weight, height and diameter. In the case of sausages, the minced preparation is inserted into casings using a hand held or automatic sausage filling machine. End products are stored under conditions of domestic freezing (about −20°C), preferably using bulk vacuum packaging, for quality control analysis (microbial growth, chemical composition, color, etc.), and retailing. Table 1 reproduces typical formulations of fish burgers based on aspects of hydrocolloid technology outlined thus far.

Table 1 Formulations of fish burgers standardized at hundred parts of fish fillet

Ingredients	A	B	C	D	E	F	G	H	I	J
Fish Fillets	100	100	100	100	100	100	100	100	100	100
Vegetables	—	—	7	—	7	—	7	—	—	—
Dried apple	—	—	—	—	—	—	—	—	7	—
Dried dates	—	—	—	—	—	—	—	—	—	7
Dried apricot	—	—	—	—	—	—	—	7	—	—
Corn starch	—	12	12	12	12	12	12	12	12	12
Milk powder	—	—	—	—	—	—	1.7	1.7	1.7	1.7
Soy protein	—	—	8	—	—	—	—	—	—	—
Bovine gelatin	—	—	—	—	1.7	—	—	—	—	—
K-Carrageenan	—	—	—	0.2	—	—	—	—	—	—
KCl	—	—	—	0.23	—	—	—	—	—	—
Citrus pectin	—	—	—	—	—	0.2	—	—	—	—
CaCl2	—	—	—	—	—	0.06	—	—	—	—
Garlic powder	—	—	0.8	—	0.8	—	0.8	0.8	0.8	0.8
Spices	0.8	0.8	—	0.8	—	0.8	—	—	—	—
Sucrose	1.7	1.7	1.7	1.7	1.7	1.7	1.7	1.7	1.7	1.7
NaCl	1.3	1.3	1.3	1.3	1.3	1.3	1.3	1.3	1.3	1.3
Black pepper	—	—	0.3	—	0.3	—	0.3	0.3	0.3	0.3
MSG	0.3	0.3	0.3	0.3	0.3	0.3	0.3	0.3	0.3	0.3
Polyphosphate	0.3	0.3	0.3	0.3	0.3	0.3	0.3	0.3	0.3	0.3
Ice water	8.5	8.5	8.5	8.5	8.5	8.5	8.5	8.5	8.5	8.5

ANALYTICAL AND ORGANOLEPTIC METHODS OF QUALITY CONTROL, AND INNOVATION IN THE DEVELOPMENT OF PROCESSED FISH PRODUCTS

Physicochemical Quality and Storage Stability of Fish Products

As for any processing operation in the food industry, the quality and storage characteristics of fish products need evaluating, and once these are deemed to be satisfactory, commercialization can be considered in earnest. Typically, assessment is implemented at regular time intervals thus removing and analyzing at ambient temperatures samples that were stored at – 20°C for a period of up to twelve months expected between manufacturing, retailing, and consumption. Standard parameters analysed for include total aerobic and coliform bacterial count, peroxide value, protein solubility, and color.[35] Based on the formulations cited in Table 1, it was found that total aerobic bacteria were reduced significantly by at least 90% of the initial load within the first three months of frozen storage. Even more dramatically, coliform counts were completely eradicated within a similar timeframe of observation.[36]

Peroxide value increased but it did not reach detectable levels of rancidity. Similarly, there was a statistically insignificant decrease in salt-soluble protein content during the storage period. In terms of the colour of raw fish products, hunter L values showed good stability hence keeping products bright prior to cooking. The storage stability of the novel embodiments may be rationalized on the basis of the effectiveness of freezing, and antimicrobial/antioxidant properties of food additives/spices.[37] Furthermore, the gelation ability of hydrocolloids reduces the reaction rates and microbial mobility within the polymeric matrix.[38] Thus, products are deemed to be acceptable within the general framework of microbial stability and non-toxicity, a result that paves the way of developing improved formulations to meet consumer expectations of eating quality characteristics.

Principles and Application of Texture Profile Analysis in the Development of Fish Products

Texture and mouthfeel remain the ultimate criteria of product acceptability by the consumer. Prediction and control of the organoleptic properties of the final product, however, is in general largely empirical. In this context, the conventional technique of compression testing has been enjoying a renewed interest since it is increasingly successful in identifying traditional or substitutive textural attributes for a broad range of foodstuffs.[39] Thus compression testing is able to differentiate between the long range (i.e., large deformation properties) of a hydrocolloid gel (e.g., table jelly or soft confectionery product), a spreadable dispersion (e.g., butter or soft processed cheese), and a very viscous embodiment (e.g., full fat yoghurt or thick vegetable soup).[40]

Application of large-deformation compression testing to the textural aspects of fish products can be implemented as follows: Frozen preparations are taken out of the domestic freezer and thawed at ambient temperature for around 30 minutes. Pan-frying is probably the most popular way of cooking and this can be carried out for 5 to 10 minutes with a little spread of oil on the pan and then allowing to cool at ambient temperature for subsequent analysis. Cooking time is determined according to experience or the manufacturer recommendations for commercially available products. Among the various texturometers, the TA.XT2 Texture Profile Analyzer of Stable Microsystems (Godalming, UK) has proved to be versatile in compression testing, which is employed by loading rectangular or cylindrical pieces of the samples onto the platen of the instrument. These can be compressed to 90% of the original height at a compression rate of 0.1 mm/s, although the choice of experimental settings is largely arbitrary and varies from product to product, usually at ambient temperature (about 24°C) for convenience.

Controlled compression testing generates a stress (force)—strain (deformation) curve, which allows extraction of several textural parameters:[41,42]

1.	firmness (N/mm) is really a small deformation property and is defined as the Young's modulus calculated from the initial slope of the curve up to a deformation of 0.2 mm for conventional samples;
2.	hardness (F m ) is the maximum force (N) at the first major discontinuity due to break or crack experienced in the sample, with the maximum value representing either a peak or a shoulder on the force/deformation profile;
3.	brittleness is the deformation (mm) or percentage strain of the first peak at the cracking point;
4.	inflectional force (F i ), which occurs at an inflection point of the curve during the compression phase, where the force goes through a minimum value following a sharp decrease and a subsequent increase;
5.	Stress ratio, which equals F i  / F m ; and
6.	adhesiveness (N mm) is defined as the negative force area of the first compression representing the work necessary to pull the compressing plunger away from the sample provided that the material exhibits stickiness during decompression.

The attributes of springiness and cohesiveness which combine measurements from the second and first compression cycle may be used to further elucidate textural aspects of the hydrocolloid matrix in the fish product.[43,44]

Sensory Evaluation with a View to “Handshaking” with Instrumental Texture

It is an observation of ours that a dividing line has emerged, which is quite rigorous, with researchers addressing the issue of novel product development opting to work in the main either on instrumental texture along the lines described in the preceding section, or sensory texture in the form of the quantitative descriptive analysis (QDA).[45,46] The aim of this treatise is to demonstrate that considerable gains can be made by considering in earnest a relationship between instrumental and sensory texture thus sharing the expertise of the two “camps,” and the remaining of this section will be composed keeping this in mind.

Fish products should undergo a preliminary hedonic screening for flavor, overall texture, moistness, and overall preference with at least 30 lay taste panelists (preferably more) to position the sensory specialist who is in charge of the project, as to the “pleasantness / unpleasantness” of the original formulation. The production development or, if necessary, reformulation cycle will then commence in earnest. Inevitably this involves rigorous evaluation for scores of sensory attributes using at least 9 trained panelists in a quantitative descriptive analysis (QDA). Eventually the number of product prototypes shall be narrowed down to a manageable subset for another (final) round of consumer sensory evaluation in order to assess the desirability of the product at the end of the road of commercial development.[47] All along, the sensory professional should pay particular attention to the design of the experimental protocol used in the investigation. Items of the test include appearance, geometry, and serving temperature of the sample, type of serving container, and carrier if needed, number of samples served per session, and if the panelists should swallow, expectorate, or rinse their mouths between trials. Once the basics of sensory settings are mastered, training of the panelists ensues for QDA. The following constitutes an example of sensory attributes, which could be described to the trained panelists as follows.[48,49]

1.	Hardness is the amount of force required to cause the sample to disintegrate between the molars. The panelist places a piece of, for example, the cylindrical sausage disk on the molars and then compresses it until rupture occurs. Standards that may be used at the two extremes of the linear scale on the score sheet are soft processed cheese and raw carrot (low and high standard, respectively).
2.	Brittleness is the extent of deformation that occurs before the sample disintegrates. The sample is placed between the molars and pressure is applied. Sample deforming before its disintegration indicates low brittleness, whereas sudden disintegration without deformation indicates high brittleness. Standards can be marshmallow (low) and raw carrot (high).
3.	Adhesiveness is the energy required to remove the sample from the roof of the mouth after chewing. The sample is chewed first, and then the mass is pressed against the roof of the mouth with the tongue and assessed. If the sample falls easily then it has low adhesiveness; whereas if it is necessary to apply force by the tongue to the mass in order to remove it this indicates high adhesiveness. Standards used are raw carrot (low) and soft processed cheese (high).

A graphical scale with low and high marks at the corresponding ends of the scale is used to assess the attributes by the panel. This type of score sheet is reproduced in Table 2, which in addition to the above includes the sensory attributes of firmness, springiness, cohesiveness, and overall acceptability.

Table 2

EXAMPLES OF DEVELOPING DESIRABLE FISH PRODUCTS BY COMBINING INSTRUMENTAL AND SENSORY TEXTURE

As mentioned earlier, successful modification of the texture, functional properties and stability (thermal, mechanical, storage, etc.) of fish products requires intelligent manipulation of proteins and polysaccharides in the mixture. Interactions of the fish protein with added hydrocolloids may lead to phase separation or synergistic phenomena that would ultimately determine the quality and acceptability of these preparations.[50]

Figure 1 illustrates the large-deformation testing profiles of selected fish burger formulations from Table 1. Preparations (A) based solely on fish muscle are able to form networks of increased mechanical strength that stretch extensively upon compression. This is due to thermal denaturation and aggregated interactions among the hydrophobic heads of the filaments of the myosin protein during cooking.[51]

Figure 1 Force-deformation data of cooked fish burger formulations indicated by the individual traces and detailed in Table 1. Products were compressed at ambient temperature (23°C) with a rate of 0.1 mm/s. An example of the derivation of the ratio of inflectional force to hardness (F _i  / F _m ) is given by the trace of formulation B.

Addition of starch imparted strong gel-like properties to the samples, which produced a clear maximum in the values of hardness upon compression (B).

Inclusion of soy maintained a strong network that can stretch extensively before deforming (C). The long texture of the soy network is due to the formation of disulphide bridges upon thermal denaturation. These facilitate cross-linking between corpuscular strands thus building up a three-dimensional structure of globular proteins.[52] In all cases, however, the elastic properties of a simple fish burger, the phase-separated topology of starch and fish protein, or the covalent structure of the soy gel are not favoured by the panelists who assigned them low sensory scores. These were 3.85 ± 0.1 out of max 7.0 in an overall acceptability test.

Hedonic acceptability was improved by preparing burgers in the presence of gelatin (E). The intermolecular associations of the protein are in the form of triple helix but unlike starch, these do not associate further to form multi-stranded particles.[53] In the absence of aggregates, a soft structure is obtained which was found to possess a positive effect on the acceptability of the product by the taste panelists (4.53 ± 0.15 out of 7.0). The above work created an envelope of structure - function relationship between the upper bound of formulations B and C, and the lower bound of formulation E.

It was sensed that designing formulations of intermediate texture could be the answer to this particular case of product development. That was accomplished by using low methoxy pectin in the presence of calcium counterions (F), and in particular milk concentrate (I). The latter preparation exhibited a relatively short proteinaceous structure (yield strain of 0.9 units), and intermediate values of hardness (yield stress of 125 kPa) in Figure 1. These imparted favourable organoleptic properties to the novel embodiment seen in the eating quality score being close to 5.3 (± 0.1).

In parallel to the consumer sensory evaluation that focuses on overall acceptability, the instrumental attributes of firmness, hardness, brittleness, etc. (described earlier under the section of controlled compression testing) were evaluated in relation to overall sensory acceptability. In general, this type of approach constitutes a step up in the use of advanced tools available to the sensory scientist / food product developer. As an example of the utility of this approach, Figure 2 summarizes the itinerary, for the instrumental attribute of firmness, of constantly improving the sensory profiling by altering strategically the formulation based on the disparate structural properties of the commercially available hydrocolloids.[54]

Figure 2 Handshaking firmness from compression testing, at conditions indicated in Fig. 1, with overall sensory desirability for the burger formulations of Table 1 (error bars indicate one standard deviation).

The above work paves the way for full implementation of descriptive analysis, which is considered as the most sophisticated tool capable of providing detailed specification of the sensory attributes. Such an interaction between instrumental texture and sensory evaluation has been attempted in the development of fish sausages.[55] Trained panelists were effective participants in the test, and unstructured line scales were used to describe the intensity of rated attributes according to the score sheet of Table 2.

Distinct organoleptic characteristics were achieved by varying primarily the starch content from 0 to 48% w/w of the amount of raw fish in the formulation. It was not possible to finalize appealing embodiments using dark muscled fish such as mackerel and tuna since they produced blackish red spots after processing and, in the end, the commercially underutilized fish muscle of Geelbeck croaker (Atractoscion aequidens) was preferred. Furthermore, taking note of the work on cooked fish burgers described in the preceding section, 3 to 4% w/w milk concentrate was added to the ingredient blend in order to improve the texture and mouthfeel of the end product.

Regarding the effect of starch content on the instrumental and sensory characteristics of formulated sausage, an example is given for the attribute of hardness in Figure 3. Experimental values were transformed into dimensionless ratios by dividing with the corresponding maximum value in order to facilitate comparisons of the two sets of data. Normalized data increased with the addition of starch indicating that the attribute is sensitive to the structuring functionality of the polysaccharide. Frying of fish sausages, which took place for several minutes at 190°C (about 375°F) causes starch gelatinisation, and the generated pasty consistency bears an effect on the results of the subsequent rheological and sensory analyses at ambient temperature.[56]

Figure 3 Instrumental and sensory hardness of formulated fish sausage as a function of starch content; rest of the formulation includes; milk concentrate (4%), sugar (1.3%), table salt (2.3%), vegetable oil (10%), water (79%), and spices (1.9%) per 100 parts of fish fillet.[55]

Regression coefficients for the instrumental and mouthfeel versions of the attribute were high (r² > 0.84), a result which emphasizes the increased sensitivity of the human palate and mechanical compression testing to the changing external stimulus of this series of samples. The above outcome allows direct comparison between the sensory perception and the instrumental texture profile analysis, as illustrated for hardness in Fig. 4. This demonstrates that instrumental hardness correlates strongly with the sensory hardness and, in accordance with Fig. 3, the magnitude of both attributes increases considerably with higher starch additions to the preparation. However, such a correlation between instrumental and sensory texture may not be always possible for attributes, or may not be that unambiguously defined leading to a low regression-coefficient value. An outcome of that nature would indicate a weakness in the customary definition of concepts in this field, or in their direct application/conversion from instrumental to sensory experimentation and vice versa. Clearly, such an event renders invalid the implementation of quantitative descriptive analysis.

Figure 4 Relationship between instrumental and sensory hardness taking into account eight sausage formulations with increasing starch content, as shown in Fig. 3; the vertical line intersection pinpoints the values of instrumental/sensory attribute of hardness at a starch content of 8% with optimum product acceptability by the consumer.[55]

Reverting to Figures 3 and 4, completion of this type of work allows implementation of affective testing towards the end of the research and product development project. Results argue that textural desirability could be optimized in formulations of fried fish sausage containing 8% w/w starch. The values of instrumental and sensory hardness related to optimum product desirability are indicated as vertical intersections in Fig. 4. Finally, overall consumer acceptability can be improved further with inclusion of selected spices in the formulation to satisfy gourmet taste.[57]

CONCLUDING REMARKS

Current definitions for quantitative measurement of food texture using large-deformation compression testing were combined with a recently developed protocol of sensory evaluation. The aim was to correct some of the perceived problems associated with the development of novel fish products. Thus, a set of interesting data was generated on the basis of the aforementioned quantitative descriptive analysis and expert modifications of fish product formulations. The latter was carried out taking advantage of the structure - function relationships of commercially available proteins and non-starchy polysaccharides. This led to a direct correlation between instrumental and sensory attributes, which controlled textural characteristics. Manipulation of texture resulted in improved organoleptic desirability of the final product via a supporting routine of affective testing. This protocol of developing processed fish products is based on principles of “materials science,” and it may be notable for work on other foodstuffs. Further advances would require consolidation of the current position by offering tangible evidence of the structural characteristics of hydrocolloids and their phase behaviour in mixtures via microscopy. This has been attempted primarily for model systems of protein and polysaccharide in the gel state. In the case of whey protein isolate and gellan gum or κ-carrageenan, protein continuous or bicontinuous structures were visualized by confocal laser scanning microscopy (CLSM).[58] Gels were subjected to large deformation analysis with patterns of flow being further visualized by CLSM. Quantitative descriptive analysis demonstrated that gel breakdown as well as serum release were responsible for the sensory properties of these gels. Similarly, light microscopy evidence of the phase inversion patterns in gelatin – maltodextrin (i.e., hydrolyzed starch) gels linked structural behaviour to mouthfeel of low fat spreads prepared with these ingredients.[59] Clearly, microscopy images in combination with instrumental and sensory texture will further enhance the quality control and likelihood of acceptance of processed fish products by the consumer.

As a final note, a dimension that merits touching upon for future reference is the inclusion of flavour in sensory quality. Quantitative correlation between flavour perception using, for example, a gas chromatograph-olfactory protocol and instrumental / sensory texture has not been attempted in earnest for processed fish materials. Literature cites chemical composition data in relation to the sensory parameters of colour, flavour and overall acceptability of fish fingers made of minced meat.[60] Another example is the inclusion of wheat fiber in minced fish to improve the water holding capacity of the composite gel, and reporting the absence of unusual flavours in the restructured product.[61] Detailed investigations of flavour encapsulation or preservation in hydrocolloid matrices upon processing and storage is a requisite for developing an advanced database of instrumental texture - sensory property.