Muscle Protein Structure-Function Relationships and Discrimination of Functionality by Multivariate Analysis

Functional (gel strength, cook loss, emulsifying, fat and water binding capacities) and physicochemical properties of mince and salt-extractable proteins were analyzed. Factor analysis identified three principal components which accounted for over 75% of data variance and distinguished between mechanically and hand-deboned meat and fish samples. Stepwise discriminant analyses classified samples with good, intermediate and poor functionality. Regression analyses yielded equations to predict functionality from physicochemical properties. Generally, samples with superior thermally induced functionality possessed (1) higher protein, lower fat and pH in the mince; (2) higher solubility and sulthydryl and lower hydrophobicity in unheated salt-extractable proteins; and (3) greater decrease in solubility and increase in hydrophobicity after heating.     

OPTIMIZATION OF THE SETTING AND COOKING CONDITIONS FOR MAKING GELS FROM PACIFIC WHITING SURIMI

Response surface methodology was used to determine the optimal setting and cooking time and temperature conditions for Pacific whiting surimi resulting in maximized gel strength, fold score, and water holding capacity. Cooking temperature was the variable that had the strongest influence on the gel quality characteristics. Level set programming, a global optimization method, gave essentially the same results as a gradient based optimization method. The results obtained by these two methods were better than those generated by the Simplex technique. Multi-objective optimization was also used to simultaneously optimize the response variables.     

Pattern Recognition of GC Profiles for Classification of Cheese Variety

Volatile components in Cheddar, Gouda, Edam, Swiss, and Parmesan cheeses were concentrated with a modified Likens-Nickerson apparatus and analyzed with a fused silica capillary GC. Stepwise discriminant analysis was applied to the 118 peaks in the resulting gas chromatograms to classify objectively cheese varieties, and most of the cheese samples were successfully assigned to the correct varieties. Discrimination between Gouda and Edam was the most difficult among all combinations of two varieties within the five cheeses. Clusters corresponding to young, mild and old cheeses were observed in the canonical plot based on the GC data of Cheddar cheese samples.     

Elimination of β-Lactoglobulin from Whey to Simulate Human Milk Protein

When the pH of cottage cheese whey was adjusted to 4.5 in the presence of 6.7 mM FeCI³, β-lactoglobulin was eliminated from the whey as a precipitate. However, the majority of immunoglobuhns were also coprecipitated. To recover immunoglobulins together with α-lactalbumin, the whey pH was adjusted to 3.0 in the presence of 4.0 mM FeCI³. After centrifugation of the whey, the supernatant contained exclusively β-lactoglobulin; other whey proteins were found in the precipitate. Excess Fe₊₊₊ in the precipitate was removed by ion exchange or by ultrafiltration. This protein concentrate had a protein composition much more similar to that of human milk whey than that of ultrafiltered whey protein concentrate.     

Hydrophobicity and Solubility of Meat Proteins and Their Relationship to Emulsifying Properties

Surface hydrophobicity (S_o) of crude salt extracts of meat was determined fluorometrically using cis-parinaric acid as a probe. Upon heating the extracts to 70°C, S_o increased two- to threefold, whereas protein solubility (s) decreased to 20%. Further heating (to 85°C) resulted in slight decreases in both S_o and s. Backwards stepwise multiple regression equations for prediction of emulsifying activity index (EAI) and emulsifying capacity (EC) were: EAI = 2.658 + 0.0001308 sS_o, and EC =−35.30 + 6.459 s + 0.001317 sS_o− 0.05463 s². S_o was most important for predicting emulsifying properties of samples with high (>50%) solubility, whereas solubility parameters were more influential for samples with low (<50%) solubility.     

SOME PROPERTIES OF MYOFIBRILLAR PROTEINS OBTAINED FROM LOW IONIC STRENGTH EXTRACTS OF WASHED MYOFIBRILS FROM PRE- AND POST-RIGOR CHICKEN PECTORAL MUSCLE

SUMMARY— Changes in extractability of the proteins associated with the fragmentation phenomenon of myofibrils in chicken pectoral muscle were studied. The results indicate that the protein fractions extracted by neutralized water from muscle residue. from which water-soluble proteins have been washed out, increase in post-rigor muscle. The extracts from pre- and post-rigor muscle were fractionated with ammonium sulfate into two fractions: the fraction precipitated by 1.7 M ammonium sulfate (Fr.1) and the supernatant (Fr. 2). Depressing effect on the onset of ATP-induced superprecipitation of trypsin-treated myosin 6 which was initially present in Fr. 2 from pre-rigor muscle decreased to a great extent in that from post-rigor muscle, whereas promotive effect on gelation of F-actin and superprecipitation of the myosin 6 which was little in Fr. 1 from pre-rigor muscle appeared in that from post-rigor muscle. It is proposed that an increasing amount of protein which indicates α-actinin activity is released along with the destruction and final dissolution of the Z-line structure during postmortem storage of chicken pectoral muscle.     

MULTIVARIATE ANALYSIS OF STRUCTURE-RELATED DATA TO EXPLAIN MILK CLOTTING ACTIVITY OF PROTEOLYTIC ENZYMES

Multivariate analysis was used for investigating the relationships between milk-clotting activity and physical/chemical properties, such as CD spectra, hydrophobicity and zeta potential, of ten proteolytic enzymes measured at six different pH values. Cluster analysis of CD data and zeta potential values classified the enzymes into five groups, i.e., three active enzyme groups and two inactive enzyme groups with respect to milk clotting activity. Classification of the enzymes into three groups, i.e., enzymes with high, medium and low milk-clotting activity, was achieved by discriminant analysis after adding the ratio of secondary structure parameters to the predictor variables. Results indicated that β-sheet, β-turn and random structure features were important for milk-clotting activity.     

Tetrathionate Protects Proteolytic Activity of Simulated Papaya Latex and Crude Papain

Sodium tetrathionate (TT) was assessed for its possible protection of proteolytic activity (PA) of rehydrated crude papain during drying and storage. The addition of 1% TT significantly decreased the loss of PA of rehydrated crude papain after being oven dried at 55°C. This protection of PA was 15–20% higher than that from metabisulfite. Crude papain with 1% TT lost 20% of PA and with metabisulfite lost 45% of PA in 13 wk at room temperature. Results suggest TT may decrease loss of PA during papaya latex processing and storage of crude papain.     

Silica-based and Polymeric Columns for Reversed-phase HPLC Analysis of Cheddar Cheese

Octadecyl polymeric (ODP) vs octadecyl silica (ODS) reversed-phase high-performance liquid chromatography (RP-HPLC) columns were compared for analytical separation of water-soluble fractions extracted from Cheddar cheese. A polystyrene divinylbenzene copolymer-based column did not resolve cheese water-soluble components. Good resolution was achieved on a vinyl alcohol copolymer ODP column as well as two ODS columns under optimized conditions of gradient elution, using increasing concentrations of aqueous acetonitrile containing ion-pair reagent. However, the ODP column had longer useful life characteristics. Use of phosphoric instead of trifluoroacetic acid as ion-pair reagent produced a more stable chromatogram baseline and may prolong column useful life. ODP-RP-HPLC could be useful to monitor ripening of Cheddar cheese samples.