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The quality of roe (ovaries) used for caviar processing is of paramount importance for obtaining high quality product. Moreover, if certain roe quality standards are not met it is impossible to process caviar at all, whereas it is still possible to process other roe type products, e.g. whole cured ovaries or bait. The two most important roe quality parame-ters are roe maturity and freshness. Other quality indices such as egg size, colour, and fluctuations in chemical composition are less important.

The best caviars are processed from freshly extracted roes. However some types of cav-iar products (mainly small size and sturdy eggs) are also processed from frozen or pre-viously salted ovaries.

2.1 OVARIES

Ovaries constitute a binary organ located symmetrically to the spinal column in the belly cavity. They have the form of flattened out tubes, which narrow towards the poste-rior end. Their colour is specific for each species and to a lesser extent depends on maturity and feeding habits. It may also differ from one specimen to another, e.g., in some extreme cases goldish sturgeon eggs or albino salmon eggs were reported.

In most cases ovaries are covered with a semi-transparent, outer elastic film (epithe-lium), which holds the fish eggs enclosed. The eggs are attached to partitions of connec-tive tissue for which the outer film serves as a stem.
Sturgeon ovaries constitute morphologically separate transversal lobes. Herring ovaries are similar. Salmon ovaries do not have distinctive transversal lobes. As herring ovaries mature the lobes are less distinct, ovary outer film is almost unnoticeable and the con-nective partitions lose fatty tissue, get thinner and even disappear.

One of the most important issues is the strength of the attachment of the egg to ovary connective tissue. It effects the possibility of obtaining singled-out eggs, i.e. granular caviar. In early stages small eggs are fully enveloped in quite fatty connective tissue (membranes) and are strongly attached to it. Immature sturgeon ovaries, unfit for screening, are used to process non-granular pressed or dry-cured caviar; so called 'payu-shaya yastikovaya ikra'. Immature salmon roe are processed into whole salted ovaries, so called 'sujiko'.

With maturation this attachment weakens and the membranes become thinner. The eggs are easily detached and can be singled out for caviar. These changes are accompanied by changes in the egg/membrane weight ratio, which is important to evaluate potential product yield, especially in processing salmon caviar.

Along the ovaries, there is a fairly large central blood vessel, which branches into a sys-tem of small transversal vessels. In chum ovaries this central blood vessel is typically located between the dorsal and ventral lines. In coho it is closer to the ventral line. The shape and weight of ovaries used for caviar depends primarily on the maturity stage and differs between species. This weight may range from 5 to 35% of body weight.

Knowledge of ovary morphology is essential in order to perform efficiently the screen-ing operation i.e. singling out eggs by means of rubbing and squeezing the ovaries through an appropriate size mesh net.

2.2 MATURITY

Table 2-1, (based on profound morphological analysis), describes ovary maturity devel-opment for salmonids. The described maturation indices can be generally applied to species other than salmonids. However, in some cases the difference is major, e.g. stur-geon eggs, as opposed to salmonid eggs, become softer, their outer shell weakens and they burst easily.

TABLE 2-1

OVARY MATURITY STAGES FOR SALMONIDS

The information in Table 2-1 relates to extracted ovaries from absolutely fresh fish. Ovary colour depends mainly on fish species. Sockeye eggs are of the brightest, reddish-orange tones; chum eggs look pale reddish with orange overtones; pink eggs are pinkish-orange etc. Ovary colours and other properties change dramatically by hour de-pending on time, temperature and storage conditions.

For caviar processing the most valuable ovaries are taken at the IV maturity stage. At the V stage the egg's outer shell is excessively thick. Obviously, there is a boundary area for stages HI and V where first grade caviar can still be processed. For some areas the best eggs are obtained from fish still in the ocean and feeding. In other areas superb roe is obtained from fish already migrating in the river, e.g. Yukon river chum. The matur-ity period and duration depends on fish species and on particular stock habitat. Sturgeon mature for the first time at the age 10-15 years, pacific salmon at the age 3-4 years. For some species maturation takes place several times per life cycle, for others e.g. pacific salmon - only once.

2.3 YIELD

Ovary weight depends on fish species, fish size, area of catch and maturity stage. There is substantial variability by specimen and year of catch. That is why the information be-low, compiled from different sources, regarding the yield of ovaries in % to female fish body weight should be treated cautiously.

Even more difficult to estimate is caviar product yield based on total landings. Firstly, because the % of females in monthly catch varies. Secondly, because fishing schedules often do not take into account maturity stages.

Typical chum and pink salmon ovaries weight vs total fish body weight is given on Fig-ure 2-1 and Figure 2-2. However, fluctuations during the season are substantial. Table 2-2 can be used for preliminary estimates.

Fishing times can not always be adjusted to obtain the best roe maturity in terms of yield. The fishing regulations and scheduling of fishing openings should take into ac-count the economic impact of taking fish with immature or overmature roe. Especially when the value of caviar may exceed the value of the flesh. Obviously all kinds of other considerations influence the decision on when it is the best time to harvest roe fish. A typical case is the chum roe fisheries, where the value of chum falls drastically towards the end of the fishing season, see Figure 2-3.

Apart from biological reasons caviar yield depends on fish handling practices from the moment of harvest to the moment when the ovaries are extracted. The best solution is to keep the fish alive until the very moment of butchering for ovary removal. This is the tradition in sturgeon caviar processing where fish are delivered alive to the processing sites and held sometimes for many days till the processing starts. Such lengthy holding times clean the intestines and get rid of unpleasant roe after-taste.

Figure 2-1

Chum Ovaries Yield

Figure 2-2

Pink Ovaries Yield

Figure 2-3

Relative Value of Chum Fisheries

TABLE 2-2

OVARIES YIELD

In lumpfish gillnet fisheries the tradition is to use roe only from living fish. Immediately after catch the fish is held vertically by the tail over a container and a slit is made from the tail end to the head. The roe slips down into a bucket with minimum impurities.

Farmed or sea-ranched fish also provide good opportunities for getting roe from living fish. For the majority of wild fish fisheries fish are handled when they are already dead. m this situation highest quality roe is obtained when fish are still in rigor mortis or be-fore any signs of autolysis. Depending on the boat holding conditions one could say that roe extracted within 6-10 hours after catch will provide for the highest grades of caviar. Practically, good results could be obtained when fish are held on ice or in Re-frigerated Sea Water (RSW) systems for up to 36 hours. When fish processing is de-layed it is advisable to extract and rinse the roe immediately after fish arrive at the plant and then keep the roe at 0°C until processing is possible. Sturgeon roe is often even screened right on the fishing grounds and then kept for many hours before transporting to the processing site for salting and packing. Roe kept inside the fish deteriorates faster. Direct contact of roe with ice affects roe quality adversely and sealed buckets or bags are advisable.

When extracted in the stage of rigor mortis 95 to 100% of the roe are of the highest grade. With signs of autolysis/ the yield of highest grade caviar drops to 75%. These numerical values relate to pacific salmon. However the trend stands for all types of roe. Very often fish landings are mixed because different fish were caught at different times. Therefore the ultimate and final decision regarding roe suitability is made visually by experienced graders who evaluate each ovary individually.

Fish butchering methods may also effect roe quality. Manual butchering and roe extrac-tion, as opposed to gutting machines, is a most labour intensive job but it provides for whole ovaries and minimum initial contamination. The particular technique may vary depending on species and fish size. The technique used in lumpfish fisheries has been described. For salmon bellies, splitting is done holding the fish horizontally over a butchering table. Knives specially hooked at the end prevent damage to the ovaries.

If these two operations are not separated the chances for contamination with slime, blood and intestine contents is very high.

When roe is extracted by means of butchering machines it is impossible to comply with those rules. The roe is intermixed with all the internal organs and the initial contamination with microorganisms may reach critical levels so that all subsequent technological measures to get rid of such contamination are doomed.
Extracted ovaries should be immediately and quickly rinsed with 2-3% cold brine. Al-though, tap water can be used, light brine makes it easier to wash off slime. Tables 2-3 and 2-4 illustrate the importance of proper handling of pacific salmon ovaries and is based on Soviet Union salmon caviar industry data.

TABLE 2-3

CHUM OVARIES GRADING RESULTS

FISH HOLDING TIME IN A COLD (+2° C) ROOM, IN HOURS	% OF OVARIES UNFIT FOR CAVIAR
8	6
20	17
35	47

TABLE 2-4

PINK OVARIES GRADING RESULTS

HOLDING CONDITIONS FOR 12 HOURS	% OF OVARIES
HOLDING CONDITIONS FOR 12 HOURS	GRADED No.l	GRADED No 2	UNFIT FOR CAVIAR
Fish held with refrigeration	30	50	20
Fish held on ice at fish/ice ratio 3:1	64	33	3
Ovaries extracted and kept at 0° C	96	4	0

Statistical data on weight loss along the processing lines are very diverse. Losses occur while screening, salting, draining, packing etc. Regular weight checking along the proc-essing line will enable the processor to determine critical operations where improve-ments can contribute to better yield. In summary, we can only suggest, that the net weight of packed caviar in % of the weight of extracted ovaries ('green weight') may range from as high as 98% to as low as 50%. Low yields signal either that the roe is immature or not fresh, or processing and handling operations are executed carelessly.

2.4 FROZEN ROE

Information on the use of frozen ovaries for caviar is confusing. Frozen ovaries are not used widely. Ovaries with delicate roe structure cannot be frozen since the eggs rupture after thawing. Processing of sturgeon caviar from frozen ovaries is unheard of and not permitted by Russian standards. Obviously/ the fishing and transportation logistics should strive for fresh roe supply for caviar. However, in many cases only frozen roe can be delivered to processing sites and the issue of their utilization is of great interest.

Use of frozen salmon roe, however in limited volumes, is known in Russia. In British Columbia and Alaska it is still in the experimental stage.

The use of frozen ovaries is prohibited by Japanese tradition even for the lesser valued product 'sujiko' which is heavily salted whole ovaries. However, it is known that sujiko of lower grades is processed from frozen round North American salmon sent to Japan. A B.C. Research study on this issue established that if appropriate handling and freezing practices are applied, a good quality, marketable product can be obtained.

Our interest in processing salmon caviar from frozen roe is heightened by existing fish-ing and transportation traditions. The roe from spring salmon caught by trolling boats are often dumped despite the fact that these boats have sufficient freezing capacities to keep the roe.

The choice of the best freezing regime for roe is a problem itself. Modest freezing speed is recommended, namely the critical freezing zone boundary (-5°C) should be achieved after 30 to 40 minutes. This can be done by putting washed and drained ovaries into sealed polyethylene bags so that the frozen roe layer is 3 to 4 cm. Frozen ovaries can also be extracted from fish frozen in the round after partial thawing of the fish.

Ultrarapid (e.g. cryogenic) freezing of roe results in large size ice crystal formation which may break up the connective tissue so that the screening process goes easier. But such freezing damages weak eggs. Before processing, roe is defrosted to -1°C. Initially the thaw drip is not significant. However, after processing, the caviar releases more 'juice' as opposed to comparable fresh roe. The colour of the eggs changes after freez-ing, lessening their redness. Overmature eggs and small size strong eggs withstand the rigor of freezing much better. The salting time for comparable lots of screened frozen ovaries, as opposed to fresh ovaries, is considerably lower - a factor of two to three times. This is presumably due to outer egg shell 'weakening' which provides for better brine penetration. Egg interior viscosity of caviar made from frozen roe is noticeably lower.

The longer ovaries are held frozen before screening the lower is the yield. Salmon ova-ries frozen for 8-10 days yield 75% after screening and 60% in final product. If frozen for 20-25 days the yields are 60 and 30% respectively. As a rule, salmon caviar proc-essed from frozen ovaries is graded as No. 2. However frozen overmature ovaries may show high yields and be graded as No. 1 product.

If the ovaries are frozen inside the fish, they should be extracted as soon as the belly flaps thaw. The best way to defrost ovaries is in a 3% brine (See Chapter 7.5. Brine concentrations are expressed as % of saturation in this manual.) solution at 5-7°C. Defro-station ends when the temperature inside the ovaries is 0 to -1°C. At a brine/ovaries ra-tio of 2/1 this is achieved within 2 hours. Screening of previously frozen eggs is done very gently. The salting time to achieve desired salinity is much shorter.

Inspite of all these negative observations organoleptic trials of comparable salmon cav-iar lots processed from fresh and frozen ovaries indicated only marginal preference for caviar processed from fresh ovaries.

The overall conclusion is that when salmon caviar is produced from good quality frozen ovaries, a somewhat lower grade of caviar is obtained. It tastes more watery, its colour is paler and technological losses are significant. The shelflife of salmon caviar proc-essed from frozen roe is much shorter.

Russian state standards allow for a number of both dry and brine salted caviar products to be processed from fresh and frozen roe: cod, sole, mackerel, sablefish, herring and other. Only larger sized egg roe is brine salted. Smaller egg sized roe is dry salted. The salting time of small eggs screened from defrosted and thawed ovaries varies and may often go as low as 30-60 seconds. Small egg size caviars made from frozen roe are usu-ally seasoned and dyed.

2.5 GRADING FRESHNESS

Grading of ovaries starts during roe extraction and after rinsing. While tearing the ova-ries apart (before screening), ovaries are checked again and graded out partially or completely. Partial grading of the ovaries consists of tearing off parts of the ovaries which for some reason are not suitable for caviar, e.g. the posterior ovary end contains small eggs or parts of the ovaries adjacent to the column, are much darker in colour, etc. Par-tial darkening is the result of local overheating while the eggs were in the belly. Cutting off the outgraded parts with knifes is not recommended because it results in many broken eggs.

The general picture of chum ovary spoilage development described below can be ap-plied to all types of ovaries. More specific regulatory grading tables can be developed for each fish species. An example of such a table for chum ovaries is given in Table 2-5. The description generally fits all salmonids. Discrepancies could be found only regarding the colour.

When ovaries or screened eggs are held before salting without refrigeration they lose quality literally by the hour. Within 2 hours eggs noticeably change. They are no longer elastic but turn soft. It is easier to smash them. If held longer they may burst easily and release egg interior yolky liquid ('juice'), which has a typical whitish colour. Further de-terioration results in a sourish smell and ovaries turn into a soft semiliquid substance with sharp unpleasant odours.

These changes develop faster the higher the temperature and are caused by enzymatic and microbiological spoilage. Enzymes continue to act after the organism dies, and break down the proteins and fats of the roe, i.e. autolysis starts. Firstly it is noticeably on the outer membrane of the eggs, which gets soft and weakens. The shape tends to lose its strict round form. Weak eggs collapse and break easily, especially during the screening process. This may result in dramatic losses. Chilling and preliminary salting of ovaries before screening may reduce these losses to some extent.

Intact ovaries properly taken from a living fish are essentially sterile. It is after they are extracted and exposed to the environment that they are contaminated. The action of en-zymes enhances the growth of all kinds of microorganisms. Yeasts, molds and bacteria are introduced through the air or tools, by the personnel or by contact with the intestines. Good manufacturing practices in caviar processing raises barriers wherever possible to initial contamination and further spoilage development by shortening processing time, lowering temperatures and keeping the highest level of sanitation.

Grading of ovaries in terms of maturity (Table 2.1) and freshness (Table 2-5) take place simultaneously. Maturity changes take place rather seasonally and depend on the area of catch. Often landings contain fish of different maturity stages and different freshness status. As with maturity, it is not practical to employ objective instant instrumental measurements or chemical examination to give an objective freshness index. Grading is done visually. An example of chum ovary grading is given in Figure 2-4.

Grading by freshness aims to separate the highest grade from lower grades of raw mate-rial. Roe of lower freshness cannot be used for processing pasteurized caviar. During pasteurization the lower grade weakened eggs may collapse and release excessive juice and unpleasant odours inside the container.

Generally speaking, if fish are not considered fit for the fresh-frozen market chances of obtaining good quality eggs are low. Table 2-3 and 2-4 describe the impact of storage time and temperature on ovary quality. However this information should serve only for reference. The ovaries should be judged on their own merits. It can happen that fish freshness is marginal, but the ovaries are still of the highest grade.

Looseness or firmness of egg attachment to the connective tissue does not characterize freshness but maturity. Extensive blood capillaries throughout the ovaries should not affect the evaluation of freshness. Localized blood clots and single eggs with deterio-rated colour, usually in the parts of ovaries adjacent to the column, do not necessarily discriminate against the whole ovary. Lumps or single eggs with deteriorated colour should be removed. Noticed excrements or other foreign matter are not considered to be detrimental to the ovary as a whole. These ovaries should undergo a second rinsing.

Grading of ovaries immediately after defrosting brings additional difficulties to making an objective judgement as there is a misleading 'fresh pale' colour while the eggs are still partly frozen. Significant deterioration in freshly thawed ovaries that had been properly frozen for 4-7 days is difficult to detect. Only slight changes in colour towards redness and weakening of membranes and connective tissue are observed.

The most strict requirements ever mentioned in the literature define that only ovaries from fish taken within 6-7 hours after capture can be used for caviar. However, these recommendations do not take into account the initial state of the fish or the holding temperature and are seldom followed in practice.

In summary only two grades of fresh roe are considered. The decision is based mainly on colour and firmness of eggs. Fish holding conditions are a key issue in caviar proc-essing. The delivery of fish to the processing plant often has complicated routes and op-timal handling conditions must be employed for salmon roe: Roe from fish stored on ice for up to 36 hours which passes the grading procedure should give Grade No. 1 caviar.

2.6 CHEMICAL COMPOSITION

The proximate chemical composition of eggs varies with fish species. As compared to fish flesh, the protein and fat content are considerably higher. The chemical composition changes drastically as maturation progresses, it depends on area of catch and has all kinds of seasonal fluctuations. As maturation progresses moisture increases and fat de-creases.

The composition of the outer membrane and the yolky interior liquid differ, the latter being higher in moisture, rich in vitamins and essential amino-acids. The nutritional value of fish eggs is higher than that of flesh of the same species. Salmon eggs contain 50 to 3/000 lU/per gram of Vitamin A, 5-25 lU/per gram of Vitamin D, 10-80 lU/per 100 grams of Vitamins B, B2, and B12, 10-20 IU/100 grams of Vitamin C. Cod roe is very rich in Vitamin B1, 300-600 IU/100 grams. Pacific salmon eggs on average contain 50% essential amino acids taken by weight of dry protein.

The following amino-acids are found in different kinds of caviar: Aspartic acid, Threonine, Serine, Glutamic acid, Proline, Cystine, Glycine, Alanine, Valine, Methion-ine, Isoleucine, Leucine, Tyrosine, Phenylalanine, Histidine, Lysine, Arginine. The dif-ference in the amounts of amino acids between caviar types is not significant.

Depending on the nature of the technological process the chemical composition of the final caviar product changes as compared to the chemical composition of the egg. As a result of salting, moisture decreases, protein and ash (salts) increases and fat content remains almost the same.

Egg fats, as compared to fish tissue fats, have higher iodine values due to high content of nonsaturated fatty adds. This is why eggs exposed to air (oxygen) tend to oxidize more rapidly than flesh. The fatty substances of the eggs contain pigments, which de-termine the particular shade of the caviar products.

Among the mineral substances of fish eggs one can list: phosphorus, potassium, chlo-ride, sulphur, sodium, calcium, magnesium, zinc, iron and manganese.
Table 2-6 gives the proximate analyses of fish eggs. The numerical range reflects fluc-tuations caused by maturity stage, area of catch, etc.

The nutritional value of caviar is further enhanced by its extremely high digestibility. It is used during postsurgical recovery, for children in extreme cases of avitaminosa. The rumours of caviares aphrodisiac properties are not scientifically substantiated.
Table 2-7 shows the proximate analysis of some caviar products. Obviously, after proc-essing the moisture content decreases and the concentration of proteins and fats increase.

This information suggests that in the past ordinary fish caviars were heavily salted. In recent years jarred, canned and pasteurized pollack and carp caviar in the market place contain 3 to 5% salt.

2.7 EGG STRUCTURE

The number of eggs in ovaries, their size, colour, shape, toughness and taste depend on fish species. Sturgeon ovaries may contain 0.2 to 4 million eggs, whereas salmon ova-ries contain 1 to 7 thousand eggs. Average chum ovaries contain three thousand eggs. The largest salmon eggs are those of Atlantic salmon, chum and chinook, which may reach 8 mm in diameter. The smallest eggs are from the roe of carp, whitefish, cod, and herring, and they range from 1 to 1.5 mm. Caviar eggs within the same species are not graded by size during processing, except for the more valuable sturgeon eggs. Sturgeon eggs are graded into three groups by size. The size is measured as the longitudinal axis of the slightly oval sturgeon egg. Grading standards are given in Table 2-8.

Within a single specimen colours are homogeneous. Sturgeon egg colours show re-markable variability between species and specimens. The range is light grey, grey, dark grey, black, grey-yellowish, grey-brownish, grey-greenish, and dark golden.
Salmonid egg colour is within the light-orange, orange-reddish, reddish-orange and red spectrum. Most of the other fish eggs are pale shades of greyish, yellowish, pinkish, greenish, and brownish.

TABLE 2-6

FISH EGG CHEMICAL COMPOSITION

FISH	CONTENT IN %
FISH	MOISTURE	PROTEIN	FAT	ASH
Caspian Sturgeon	77-65	17-32	11-18	1-2.2
Chum	50-56	27-35	12-20	1.5-1.7
Pink	50-60	23-38	10-15	1.9-2.0
Sockeye	56-58	20-29	10-13	0.7-1.7
Chinook	51-70	21-34	8-18	1.2-1.9
Roach	66-67	24-26	1.7-3.0	1.5-3.0
Pike	64-67	14-27	1.5-2.4	1.2-3.0
Carp	70-75	17-24	1.5-2.0	1.4-2.6
Sander	60-71	18-26	1-11	1.5-3.1
Cod	78-80	16-20	0.3-0.7	1.7-2.3
Pollack	80-86	11-15	1.8-2.5	1.5-1.9
Herring	70-80	14-25	0.7-4.8	1.8-3.7
Flounder	70-76	17-24	0.5-1.8	2.0-2.7
Mackerel	65-71	21-30	4.4-6.3	1.0-1.9
Lumpfish	80-85	10-12	4.4-4.7	1.5-2.0

2.0 ROE

2.1 OVARIES

2.2 MATURITY

TABLE 2-1

OVARY MATURITY STAGES FOR SALMONIDS

2.3 YIELD

Figure 2-1

Chum Ovaries Yield

Figure 2-2

Pink Ovaries Yield