ON THE KEEPING QUALITY AND NUTRITIVE VALUE OF PORK

Transcription

1 METHODS USED I N DETERMINING THE EFFECT OF FREEZING AND STORAGE ON THE KEEPING QUALITY AND NUTRITIVE VALUE OF PORK The f l a s h and f a t of pork is r e l a t i v e l y unstable when held i n storage a t O F, for more than a few morlths, Furthermom, when subjected t o the action o f oxygen, enzymes and bacteria, i t s a b i l i t y t o r e t a i n n u t r i e n t s and prevent quality changes is f i r t h c r hampered, I n order t o have a complete and t r u e picture of the changes t h n t take placc in the quality and n u t r i t i v e value of pork, t h e investigator must not be s a t i s f i c d with a f e w single p r a c t i c a l tests. A nore complete analysis requires numerous physical, chemical, and organoleptic mcthods of t e s t i n g. With t h i s i n mind, I have grouped some o f t h e more important methods undor two large headings: 1. Subjective Mothode and 2, Objective Methods. PIETHODG: Perhaps one of the most desirable techniques of measuring these two all-important factor8 in fresh and frozen pork is through visual observation. A t r a i n e d eye mag r e g i s t e r much i n a r e l a t i v e l y short time by a c t u a l l y obswving t h c meat f o r such changes as color, aroma, texture, nature of the f a t, e t c On prolonged s t o r a g o, the frcsh, pink color of pork changes t o gray. A t the same time odors ofton develop. Them changes, as well as dehydration spots, glazed areas, and loss of moisture can add much t o determining the acceptabilit y of t h e product upon rcnoval f'rom zero storage, Moisture l o s s f'rom frozen pork may be determined by the periodic weight record method, thuo serving as an index t o the effectiveness o f t h e protective cover used during the storage period.. Organoleptic t e s t i n g has been ueed i n meat p a l a t a b i l i t y studies f o r many years. The factors here rated a r e based on the opinions of t h e i n v e s t i gators. The score given is usually 8 physiological reaction which i n turn is a r e s u l t of past t r a i n i n g, experience, personal preference, o r powers of perception. This method of t e s t i n g i s aubjective since the individual is required to go through a mental process in giving an opinion a8 t o q u a l i t a t i v e and quantitative values of the characters under study. A p a l a t a b i l i t y committee maybe used t o r a t e or score quality factors o r quality changes in pork during t h e storage l i f e. The factors more commonly r a t e d by such a committee are: flavor, appearance, juiciness, tenderness, texture, and rancidity. One of the f i r s t requirements or" t h i s type of t e s t i n g, however, i s t o e s t a b l i s h a panel of t r a i n e d organoleptic t a s t e r s that w i l l give The Meat Board has found t h e "paired-eating method" reproducible r e s u l t s preferable t o Judging o r scoring. I n t h i s method members of the panel a r e provided with paired samples o f pork and a r e asked t o r a t e the samples b y comparison with one another. The samples under coneideration should d i f f e r i n only one important variable o r treatment. One of the d i f f i c u l t i e s of the panel method.

2 135. of t e s t i n g, as pointed out by Dr. Lowe, i s the separation of the p a l a t a b i l i t y factors since it takes a great deal o f mental discipline and t r a i n i n g t o separate and c l e a r l y evaluate them individually. However, when the panel method of t e s t i n g is used under controlled conditions and the r e s u l t s a r e t r e a t e d s t a t i s t i c a l l y, it i s one o f t h e simplest and quickest methods of quality evaluation. OBJECTrVE METHODS: Objective methods 0;' measuring quality and n u t r i t i v e retention in pork a r e those based on recognized standard s c i e n t i f i c t e s t s. They represent the modern idea in measuring quality control, because the human element ( a t t i tude of the investigator) has been excluded. These methods can be divided i n t o the following four groups: Physical Methods, Chemical Methods, Micro-Methods and S t a t i o t i c a l Analysie. Physical Methods: The physical method most often used in meat research i s the WarnerB r a t z l e r Shear for measuring tenderneos. These a r e two other recognized methods o f determining tenderness of neat. These a r e the p a l a t a b i l i t y methods and chemical analyses. However, the shear method has been the b a s i s f o r much o f the voluminous l i t e r a t u r e on tenderneos in meat. Since t h i s method was s o ably discussed a t our previous meeting, it i s oufficient to repeat t h a t the reoults o f t h i s objective t e s t show a highly eignificant correlation with the scoring o f a committee on p a l a t a b i l i t y. Juiciness i n pork i o a condition r e s u l t i n g from the presence o f n a t u r a l expressible l i q u i d s in t h e meat and r e f e r s t o the amount and character of these l i q u i d s. Since there i s considerable l o s s of moisture when pork i s Frozen, juicinees i s a very important factor i n deciding quality. Press f l u i d determinations are accomplished with the a i d of a Pressometer, o r the Carver Press. This mechanical device requires a weighed quantity of meat t o be pressed and again weighed t o determine the quantity of moioture removed. Here again there i s a close correlation between the a b i l i t y of tb pork t i s s u e t o hold l i q u i d and the juiciness of the cooked meat as evaluated by the p a l a t a b i l i t y committee. Previous research has indicated t h a t deterioration o f pork takes place most rapidly i n the f b t t y portion of the meat. Consequently, the f a t content markedly influences the storage l i f e. Since the nature of pork f a t shovs evidence of deterioration more rapidly in the form of rancidity and o f f color, an instrument such as the Liporneter may be an i n d i r e c t method o f determining quality since it w i l l indicate t h e f a t content of the pork sample. This instrument i s a r a t h e r simple apparatus which w i l l det&mine the f a t cont e n t of ground pork in three t o five minutes, The instrument i s calibrated in terms o f percent of fat and gives a d i r e c t reading f o r the sample. The l i p ometer operates on the principle or" a hydrometer. However, instead of determining density o f the f l u i d in which it f l o a t s, cold tap water is used t o determine the f a t content i n a d e f i n i t e volume of sample contatned within its measuring chamber. This instrument has been shown t o be h i g u y accurate *om comparisons made with the common e t h e r extraction method on hundreds of meat samples

3 136. Changes in the hydrogen-ion concentration of pork a l s o may furnish considerable infolrmation, The Beclansn pe meter i o being used in meat and food laboratories for determining pe values. The pr value frequently Indicates the basis f o r evaluating changes brought about by the presence of such materials as enzymes, bacteria, and oxygen i n t h e pork t i s s u e. Chemical Methods: There a r e numerous chemical tests t h a t can be made on pork t o determine the e f f e c t of Freezing and storage. It i s not my intent t o discuss them a l l, However, I would like t o name a f ew methode that have a t t r a c t e d my a t t e n t i o n while exaaining the l i t e r a t u r e. Rancidity is of foremost i n t e r e s t t o those confronted w i t h pork storage, The Watts Method and Conrad Method have received xuch use when determining t h i s change i n pork f a t. There i s some evidence t h a t the Watts Method w i l l give higher peroxide extractions and it i a being used more extens i v e l y in pork s t u d i e s. Furthermore, the Occurrence o f peroxides i n r a w fht coincides closely w i t h rancid flavor i n the cooked Pat. Regardlees of the method used, r e s u l t s of chemical analysis of the P a t, in many ways, are i n l i n e with the findings of t h e p a l a t a b i l i t y committee. It i s apparent t h a t simple freezing releases a greater amount of protein than non-protein nitrogen. Therefore t h i s chemical analysis i s of great importance i n determining the n u t r i t i v e value of pork t i s s u e under observation, both before and a f t e r fl-eezing. The exact methods f o r determining the presence or absence o f nitrogenous materials may be found in the chemical report presented l a s t year by D r. Dan Brady, and I s h a l l not repeat them a t t h i s time, The vitamin content of pork haa received wide i n t e r e s t and publicity since pork is a good source of the B-complex vitamins. The l i t e r a t u r e makes reference t o many methods of vitamin analysis. However, the Fluorometric Determination Method and the Microbiological Assay Methods a r e receiving much a t t e n t i o n and appears to be s a t i s f a c t c r y i n recording v i t C m i n changes i n pork tissue. The determination of enzymatic a c t i v i t y has not been used extenaively as a method of measuring q u a l i t y and n u t r i t i v e retention in frozen pork. However, It ha8 been established that fresh meat t i s s u e contains many enzymes, t w o of which a r e oxidative and proteolytic. These enzymes play a major r o l e i n bringing about changes i n flavor, s t r u c t u r e, e t c. Recent investigationo have shown t b t several members of the vitamin B-complex group a r e constituents o f important enzyme systems. I n l i g h t of these facts, t h e presence of enzymes w i l l g r e a t l y influence the storage l i f e and n u t r i t i v e value of pork and a r e no doubt conducive to numerous other q u a l i t y changes. Sane enzymes can be c r y s t a l l i z e d and t h e i r presence may be determined by t h i s method, while others require a more s p e c i f i c chemical treatment. Micro -Methods : The presence of large numbers o f microorganisme in fresh and frozen pork is o f considerable importance i n determining the storage l i f e and retent i o n o f n u t r i e n t s p r i o r t o freezing and during zero storage. It has been

4 137. 1#imw pointed out that the prese ious microorganisms not only brings about more rapid d e t e r i o r a t i o n a content, but that these l i v i n g organisms influence the kind an8 am kf enzyme a c t i v i t y. Furthermore, the presence of such biological materials are extremely i n f l u e n t i a l i n bringing about undesirable changes i n texture and flavor. The p l a t e count method f o r determining numbers of organisms has been used and found t o be very s a t i s f a c t o r y. Specific types of agar a r e used t o determine the various proteolytic, saccroyltic, or l i p o l y t i c types of organisms i n pork t i s s u e. Histological studies as a method of determining q u a l i t y changes are r e l a t i v e l y new t o the f i e l d of meats. This method is used somewhat indirectly t o evaluate q u a l i t y changes. Histological techniques are most often used t o study the c h a r a c t e r i s t i c s of muscle structure, proportion of connective t i s s u e, and deposition of f a t i n the muscle. Data collected from such studies may be used t o explain some of the changes, such a s those which take place i n tenderness and loss of moisture upon freezing and thawing. S t a t ist i c a l A n a l s s is : Every laboratory engaged i n food research encounters the problem of how best t o evaluate data collected on the product under observation. Since objective tests are f e w and limited i n t h e i r application, w e must often depend upon the rating of a t a s t i n g panel f o r c e r t a i n factors. When data of t h i s nature a r e collected from a trained organoleptic panel, they should be t r e a t e d s t a t i s t i c a l l y t o more accurately measure the consistency and discrimination of each judge, This is usually accomplished by submitting the data t o an analysis of variance and co-variance. CHAIRMAN TOMHAVE: Thank you, Professor Henrickson. The discussion on t h i s topic w i l l be led by one of the newer members of this group, Professor Robert A. EHgar, of Virginia Polytechnic Inst i t u t e. MR. EDGAR: Thank you, M r. Tomhave. f n. a d d i t i o n t o my maw d u t i e s at Virginia Polytechnic Institute, I have t o teach one m e a t s course, So I f e e l very fortunate i n making t h i s t r i p. You might be interested t o know that the plans f o r a research building a r e i n t h e hands of t h e a r c h i t e c t. W e do hope t o get some space for a meats laboratory. I a m sure we enjoyed Mr. Henrickson s excellent presentation o f the subject and I am sure t h e r e should be a few questions that we could take up a t t h i s time. 14R. KEW: We a l s o read i n the National Provisioner about the lipometer, so we bought one and if any of you need one we w i l l s e l l it rather cheaply. It bas been our experience, a t least with my technique, that it does not work out as w e l l as the manufacturer claimed it would. But I did not trust n g ~technique and I exchanged samples w i t h an

5 employee of Steak and Shake, one of those hamburger restaurants that uses it commercielly. He ran the potentiometer samples with the m e a t I gave him and I used the l i p m e t e r on the samples he gave me. W e did not check a t all, I 8 l S O ran ether e x t r a c t s on his samples and on my samples, and we did not check t h e r e, So if you are figuring on using a lipometer for future experimental work you had b e t t e r imprope the technfrlue. MR. RRADY: H6w cheap do you want t o s e l l i t? We are waiting f o r somebody t o want t o get r i d of one, MR. KEW: MR. B U U : Talk t o Mr. Bull, He w i l l s e l l it t o you. Half price. MR. WANDERSTOCK: Have 8ny of you tried B e l l o w ' s suggested method of determining tenderness, g e t t i n g 8 set size l i t t l e square of mat and c u t t i n g it up and counting the number of chews and when you reach the point where you a r e supposed t o have a so-called insoluble residue you etop counting, and then you continue and you decide how many more chews you will need before t h e sample disappears. The &me Economics folks a t Cornell have been trying. I am completely d i s s a t i s f i e d with it myself because I cannot t e l l when I have reached an insoluble residue. Can any of you? Kline have you t r i e d a t &. IOW8? MR. KLINE: No, we have not. MR. WEUINOTON: I think it is a p r e t t y good method. MEt. DEATHIWGX: Mr, C h i m a n, I have not wed it, but own objection t o it i s t h e one that t b y haye raised, that you w e an a r b i t r a r y number of chews as a measure of tenderness and you introduce negative tenderness which cannot be analyzed mathematically. sub,ject? MR, EDGAR: Are there any other comments on t h i s MR. BRADY: PIr. Wumem hss been working on t h e subb r a t z l e r ' s idea of t r y i n g things out ject of rancidity. I like while they are s t i l l new and we a r e just g e t t i n g interested i n working on it and maybe some of you folks w i l l want t o work on it and get your r e s u l t s ou before we do. Is there d e t e r i o r a t i o n going on i n bone? It i s our observation that i n pork chops the odor is not so much i n the separable fat as i n t h e bone t i s s u e. ETas anybody b d a similar =per ience I? &. MR, SUIZBACHER: I have not noticed w h a t you mentioned p a r t i c u l a r l y, but w e have run a l o t of checks on frozen boneless pork r o a s t s and there was p l e n e of off flavor in the f a t. MR. BRADY: In the bone? MR. SULZBACBER: No, i n t h e flat of the pork r o a s t s, i n r o a s t s that were boned before they were roasted.

6 139, m.. BRADY: These a r e chops. If you take off the f a t neither. - have a high peroxide value o r a r e objectionable from t h e *aste standpoint but from an odor standpoint they d e f i n i t e l y a r e o f f odor. MR. SULZBACHER: A t what temperature were they stored? MR. B W : A t aw temperature you want, It fluctuated between zero and 10. Zero i s the one you a r e thinking about p a r t i c u l a r l y. MR. EDGAR: Are there any more questions or discussions? not, I w i l l turn it back t o Mr. Tomhave. If CHAIRMAN TOMBAVE: The next topic is one that you have a l l been waiting f o r. It is " F a c i l i t i e s and Quipment Needed f o r a Modern Research Laboratory." This topic w i l l be presented by Mr. W. L. Sulzbacher of the United S t a t e s Department of Agriculture. ###