Selecting Equipment for Producing Farm-Made Aquafeeds

SELECTING EQUIPMENT FOR PRODUCING FARM-MADE AQUAFEEDS John Wood

Grain and Food Processing Section Natural Resources Institute Central Ave., Chatham Maritime, Kent ME4 4TB, U.K.

WOOD, J. 1993. Selecting equipment for producing farm-made aquafeeds, p. 135-147.In M.B. New, A.G.J. Tacon and I. Csavas (eds.) Farm-made aquafeeds. Proceedings of the FAO/AADCP Regional Expert Consultation on Farm-Made Aquafeeds, 14-18 December 1992, Bangkok, Thailand. FAO-RAPA/AADCP, Bangkok, Thailand, 434 p.

INTRODUCTION

When addressing the subject of preparing feeds for fish it is important to recognise that we are in fact seeking to prepare a foodstuff with specific nutritional and physical properties to meet the differing feeding habits of a range of aquatic consumers. The purpose of the feed manufacturing process is therefore to prepare a food which, as far as possible, meets the gastronomic habits of the target consumer. The need to prepare feeds for slow and fast feeders, water surface, mid water or bottom feeding species has been well recognised.

If a farmer is to be successful in feed preparation it is important that he examines the options available to him. In practice, most farmers have come to believe that pelleted feed is the most desirable since this is the feed form which has resulted in high yields on what are perceived to be financially successful large commercial fish farms. This is an understandable conclusion to make but its validity on a nutritional and practical basis still requires solid confirmation for semi-intensive culture. Nevertheless, in this paper we will consider the factors affecting the selection of equipment, principally for making feeds of high water stability in pellet or noodle form, since these types of feed potentially enable the maximum number of consumers to be fed at any one time. This paper will outline the principles behind equipment selection, and in particular comment on the properties of feed raw materials which will influence such decisions.

WHAT DO FARMERS WANT?

In seeking to meet the requirements of the fish we must also examine the requirements of the farmer. What are his objectives and are they achievable? The two may not necessarily be compatible in all cases. Annex 1 summarises the primary objectives of the farmer concerning feed preparation, but the degree to which they are achievable will vary from farm to farm, region to region and country to country. There is no single solution that will be practical and cost effective for all farm-made aquafeeds. We are assuming that the farmer already has a feeding strategy but wishes to improve upon it. FACTORS INFLUENCING THE SELECTION

AND INSTALLATION OF FEED PROCESSING EQUIPMENT

The supplementary feeding of cultured fish has become an established practice in many parts of the world and numerous designs and sizes of machines have been used for farm and commercial feed manufacture. Some farmers have made wise choices while others have regretted expenditure on equipment which has failed to perform adequately with the raw materials available, or was of an inappropriate capacity.

If a farmer is starting a new venture there are important factors to be evaluated before any selection of specific equipment should be considered. The response to their evaluation will then form the framework for determining the machinery requirements to meet the feed production objectives within the financial resources available (see Annex 2).

This evaluation of interacting factors must be conducted with an understanding of the physical and functional properties of the raw materials available. These aspects will be discussed in more detail later in this paper.

PROCESSING EQUIPMENT OPTIONS

There are many and various options for processing equipment for aquafeed processing, as can be seen from the practices of aquaculturists in any locality. Processing equipment options include electric or petrol/diesel engine driven machinery, and also the use of hands and feet. The most common processing operations can be summarised as:

 raw material size reduction;  raw material blending;  feed forming;  feed drying.

The range of equipment options within each processing operation are summarised in Table 1. It is not appropriate to describe these machinery options in detail since almost all are well known and specific details can be obtained from manufacturers.

Table 1. Options for feed processing equipment Process operation Equipment Raw material/product Size reduction Mortar and pestle dry or moist grinding or blending Mincer wet materialse.g. trash fish/offals Hammer mill coarse-fine dry materials Plate mill coarse-fine dry materials Blending Physical Hand for small quantities variable efficiency Feet Mechanical mixers Bowl moist doughs Horizontal dry powders or moist crumbs Vertical dry powders Forming Hand dough ball Mincer moist noodles Pelleter dry pellets Cooker extruder semi-moist/dry pellets or noodles Drying Solar variable efficiency Mechanical controlled drying

The choice of equipment will be limited firstly by financial resources, secondly by the desired water stability of the feed (and thus raw materials availability), and thirdly by the required scale of feed manufacture. However, on the assumption that finance is not limiting and all forms of machinery are potentially available, then the factor which will govern machinery choice is the spectrum of raw materials on offer for feed formulation and manufacture.

FUNCTIONAL PROPERTIES OF FEED RAW MATERIALS

Commercial fish feed manufacture is predominantly associated with the processing of dry ingredients and the manufacture of a dry product. This is not necessarily the case for farm feed manufacture. Commercial processors require dry products for long term storage and transport. Farm feeds can utilise local raw materials which may be:

 high in moisture and of short shelf life;  of insufficient quantity to become commercially viable;  grown on the farm or be a byproduct of local agriculture;  available during certain seasons only;  having functional properties which have not been damaged through industrial pre- treatment.

The question which must then be asked is: “In what way can the nutritional and physical characteristics of the raw materials available meet the desired nutritional requirements of the fish to be farmed, and be in a form which will stimulate feed intake and be water stable throughout the feeding period?”

To enable this question to be addressed we should consider the general functional properties of feed nutrients and the effect which moist heat is likely to have on them. The functional properties of raw materials, or more specifically of feed nutrients, are those which affect the ability of feed materials to:

 cross bond with each other;  alter their viscosity characteristics;  change from granular to plastic consistency;  release bound moisture;  induce water stability.

The effect of moist heat on the functional properties of feed raw materials is important since this is the kind of treatment which many are subjected to during processing before they, or their byproducts, are actually considered as raw materials for fish feed (or other animal feed).

The important functional properties of the major nutrients are summarised in Table 2. These properties are, of necessity, expressed in general terms since there are differences in specific properties depending upon the source of the nutrient. From Table 2 it is evident that the nutrients with the most important functional properties are the proteins and the starches. In most circumstances, both nutrients will also be present in high proportion in the mixed diet and therefore have the potential to significantly alter its properties. Let us examine the functional properties of these two nutrients in a little more detail.

Table 2. Functional properties of feed nutrients Change in functional Nutrient Normal state Effect of moist heat property Water liquid vapourization energy transfer colloidal fibrous Proteins denaturing soluble/hydrable to insoluble globular viscous insoluble granule to soluble Starches inert granules gelatinisation gel some cross bonding with difficult to extract with Fats liquid or solid starch amylose organic solvents Fibre fibrous minimal minimal reaction with lysine Sugars soluble solid or liquid minimal caramelization soluble or insoluble Minerals minimal minimal solid soluble or insoluble Vitamins some heat labile minimal solids

Starches

In their native state starches, whether from cereal or root crops are found in the form of starch granules which are essentially inert when placed in cold water. They resist water absorption, and there is minimal adhesion between granules. In this form starches are also of low digestibility to aquaspecies, and have minimal properties for binding other feed components. It is only when starches are heated in water, causing the granules to rupture and gelatinise forming viscous pastes and gels, that starch has desirable properties for binding feeds. However, since the starch has also become more soluble during the gelatinisation process (a property which is retained after rapid starch drying), feeds bound with gelatinised starch alone will disintegrate as the feed hydrates and continues to absorb water, although the degree of binding is considerably better than when feeds contain no gelatinised starch.

Proteins

In their native or natural form, proteins associated with plants tend to be “globular” in shape whereas animal proteins are more characteristically “fibrous” in form. Apart from those proteins which are totally insoluble, such as those comprising wool, silk and hair, proteins are soluble in water, salt solutions or mild alkaline or acid solutions. When subjected to heating, proteins tend to coagulate or denature. This is a process which is well recognised during the cooking of egg albumin, when the raw soluble protein is converted to an irreversibly insoluble protein gel.

PROCESSING OPTIONS

To illustrate the potential interactions of raw materials let us examine what processing options could be available to a farmer for fish feed production. For example, let us consider the use of three raw materials potentially available in many developing countries i.e. trash fish, sun dried cassava and full fat soya beans. These raw materials may be described in the following way:

 trash fish: hydrated, fibrous protein, with some fat associated, but no starch;  cassava: non-hydrated starch granules with little protein or fat;  full fat soya beans: non-hydrated globular protein with high association with fat and low in starch.

We will assume that each raw material will be used at the same dry matter level in each feed, and that the blend of raw materials will meet the desired nutritional requirements of the culture system being operated. The oil present in the soya beans is a required nutrient for the diet.

Option 1

Let us assume a process whereby all three raw materials are treated individually as industrial agro-products for processing and storage. They will then be blended to form a feed of the desired nutrient specification.

EFFECT OF PROCESS ON RAW MATERIAL PROCESS OPTION FEED BINDING Hot air dried to fish meal Trash fish (souble Loss of ability to cross link (coagulated protein) (denatured protein) with other proteins protein) Cassava (inert No further processing (inert Inert granules with no gelling granules) granules) chractersisitcs Soya beans Oil expelling; toasting of soya meal Loss of ability to cross link (hydratable protein) (coagulated protein) with other proteins

Result: Three separate raw materials with no inherent ability to bond with each other. These materials will require a binder and careful steam conditioning to partially gelatinise the cassava before any degree of binding between particles can be obtained.

Option 2

EFFECT OF PROCESS RAW MATERIAL PROCESS OPTION ON FEED BINDING Sun dried to produce fishmeal Trash fish (soluble Partial loss of ability to cross (coagulated protein) (partially protein) link with other proteins denatured) Cassava (inert Viscous base for aiding feed Cook in water (gelatinised starch) granules) binding Soya beans Oil expelling; toasting of soya meal Loss of ability to cross link (hydratable protein) (coagulated orotein) with other protines

Result: Improved stability of the feed due to partial hydration of some fish proteins and viscosity of gelatinised starch. Heat denatured soya proteins are inert and add little to feed stability.(Note: Even slow sun drying results inpartial denaturation of fish proteins such that rehydration does not result in the reformation of colloidal protein material).

Option 3

RAW EFFECT OF PROCESS ON FEED PROCESS OPTION MATERIAL BINDING Trash Fish (soluble protein) Blend the materials Formation of intermeshing matrix of proteins Cassava together and co-extrude and starch which are respectively denatured (inert granules) while heating and gelatinished simultaneously Soya beans (hydralable protein)

Result: This process will give the most effective bonding between the feed components, and thus the maximum feed stability. The process is in effect that which occurs during the process of cooker extrusion, and is the reason why this process has become so popular amongst commercial fish feed manufacturers. Furthermore, when using full fat soya as a raw material, the process enables the destruction of the trypsin inhibitors which would otherwise significantly depress protein digestion and assimilation by the fish. A further advantage of this form of processing is that it can incorporate wet fish as an ingredient into the feed mixture without the need for pre-drying, or the need to extract the oil from soya beans prior to their use.

ARE THESE METHODS APPROPRIATE FOR FARM-SCALE AQUAFEED MANUFACTURE?

The foregoing options illustrate the desirability for the controlled processing of protein- and starch-containing raw materials by methods which will maximise the effects of their functional properties. Feed materials must be examined in terms of their physical or functional properties and not solely as sources of nutrients.

On many fish farms, feeds are being prepared which take into account the factors discussed above. The benefits of cooking starchy bases such as cassava or rice have been recognised, both for developing the viscous gelatinisation of starch and the resulting improvement in digestibility.

However, the stability of formulated feeds which include cooked starches may also be due to a degree of starch retrogradation during cooling and sun drying. During retrogradation, starch gels tend to lose their consistency as starch molecules and form into crystalline structures (for example, starch retrogradation is often associated with the staling of bread). Once a starch has retrograded it is often more difficult to solubilise, and is less readily hydrolysed by enzymes. From a fish feed perspective therefore, starch retrogradation in association with a protein matrix may enhance feed resistance to disintegration in water. The negative effect will be reduced starch digestibility.

Where farmers use trash fish as their base, they are introducing a valuable source of both nutrients and functional characteristics to the feed. For example: a Thai farmer produced his own feed for freshwater prawns from the following ingredients: wet trash fish (44.4%), fish meal (13.3%), rice bran (6.8%), soya meal (8.9%), poultry feed (13.3%), and broken rice (13.3%). The rice was cooked to a thick paste and then mixed with the ground dry ingredients and the minced trash fish. The moist dough was then formed into strands through a mincer die plate, and the product sun dried on a concrete pad. The dried feed, which had a water stability of more than 24 hours in static water before disintegration took place, was bound with gelatinised and partially retrograded starch and by the matrix of partially denatured fish proteins produced during sun drying. Of particular interest is the addition of poultry feed. The farmer commented that it had been added to the feed mix to overcome the tendency of the fibrous rice bran to break the structure of the pellet during drying. Practically and nutritionally, the farmer may have had the same success by removing the rice bran and poultry feed from the diet and replacing them by soya meal and broken rice.

The process used in the preparation of this feed was quite labour intensive but, since the farmer was able to obtain most of his dry materials in a pre-ground form, his machinery requirements were reduced to a mincer and a simple heated bowl for cooking the rice. The mincer also served as the device for shaping the feed dough into long strands for sun drying prior to crumbling to feeding size pellets, and for storage.

This situation is, however, not typical of fishfarms which are situated away from coastal regions, where supplies of trash fish are non-existent. The only ingredients available may be the byproducts of other agro-industries which have heat treated the materials and denatured the proteins during processing, e.g. in oilseed cakes. Under these circumstances farmers may be able to obtain sufficient raw materials to meet the nutrient requirement of the culture system being operated, but have few materials which will help in developing any degree of water stability. The most sophisticated machinery will be of little use to the farmer unless he is able to obtain additional raw materials to induce binding, while maintaining the nutritional integrity of the desired feed.

ENVIRONMENTAL ASPECTS

As aquaculture expands throughout the world there is a requirement that farmers use their water resources wisely. This applies not only for the protection of their own stock, but for the protection of those who will abstract pond discharge waters for other agricultural uses, and also for the protection of the consumers of cultured species.

One of the first environmental requirements of an aquaculture farm is to maintain the quality of the aquatic environment by attempting to ensure that feed added to the pond reaches the target animal. This is the purpose of preparing water stable feeds.

A further requirement is to ensure the microbiological safety of aquatic feeding systems. Since many animal proteins are associated with potential pathogens such as salmonella, it is desirable that animal (including fish) proteins should be pasteurised before they are ingested by cultured fish. This is particularly important should the trash fish have been grown in septic ponds or other water courses potentially contaminated with faecal material. Similarly animal viscera, such as poultry offal, should also be treated before it is consumed by fish or other aquatic species. At the moment, few farm feed processors have the facilities to pasteurise protein material of this kind while including it as valuable nutrients and functional protein within feeds.

There is therefore a need to develop low cost farm scale feed processing equipment which will enable raw materials to be processed to produce feeds with acceptable microbiological and water stability characteristics. Of particular benefit would be a heated die plate for attachment to a mincer or similar feed forming machine which would act as a feed pasteurisation unit while also developing a degree of starch gelatinisation and protein denaturation. However, such a device could not replace the functions of a cooker extruder.

CONCLUSIONS

In presenting the above information an attempt has been made to demonstrate that the selection of machinery for the manufacture of farm made aquafeeds is not a simple exercise of selecting items from a catalogue in accordance with the quantity of feed desired. It is important that machinery is selected in relation to the properties of the raw materials available for formulating and processing. We are aware of what is desirable, but the task is to select the most appropriate equipment for use with non-ideal raw materials. This challenge will be much greater for some farmers than others.

Annex 1. Primary objectives of a farmer concerning feed preparation Potential for Objectives achievement Prepare feeds of ideal nutritional and physical quality which are Maybe cheaper than existing feeds Use raw materials which are locally and constantly available, Doubtful Produce feeds that are attractive and non-polluting Possibly Utilize processing equipment which has low capital and running Perhaps costs and is available locally Take minimal time and effort for processing Uncertain Have technology which is known only to him, is specific to his unlikely needs, and gives him an advantage over competitors Have a technology which is operable by family members Hopefully

Annex 2. Preliminary factors for quantifying desired aquafeed production capability

Identify and evaluate the following:

 target animals and their feeding behaviour;  raw material availability and continuity of supply;  formulation options;  feasibility of obtaining the desired feed conversion and crop yield;  output of feed required in relation to fish growth phase;  desired frequency of manufacture in relation to fish growth phase;  characteristics of the proposed site: access, power supply and its reliability. building design, storage facilities for raw materials and finished feeds, security:  desired lifespan of equipment;  possible future developments/expansion on site;  locally made or imported equipment;  process equipment options, flexibility, power requirements;  compatibility of options for formulations and equipment;  access to finance.