Extent of damage to amino acid availability of whey protein heated with sugar.

The effect of heat treatments, at various water activities (aW), on digestibility and on the availabilities of amino acids of whey protein samples in the presence of lactose was estimated by an in vitro digestion method with continuous dialysis. Four aW (0.3, 0.5, 0.7 and 0.97), three temperatures (75, 100 and 121 degrees C) and three heating periods (50, 500 and 5000 s) were selected. The initial lysine:lactose molar ratio was 1:1. Amino acid profiles showed that excessive heating of whey (121 degrees C, 5000 s) destroyed a significant proportion of cystine at all aW, lysine at aW 0.3, 0.5 and 0.7, and arginine at aW 0.5 and 0.7. At aW 0.3, 0.5 and 0.7, protein digestibility decreased (P less than 0.05) as the temperature increased from 75 to 121 degrees C for a heating period of 5000 s, and as the heating time was prolonged, from 500 to 5000 s at 121 degrees C. Excessive heating also decreased (P less than 0.05) the availabilities of all amino acids at aW 0.3, 0.5 and 0.7. The availabilities of lysine, proline, aspartic acid, glutamic acid, threonine, alanine, glycine and serine were particularly affected. Severe heating at aW 0.97 did not seem to favour the Maillard reaction, but the availabilities of cystine, tyrosine and arginine were decreased, probably as a result of structural modifications of the protein upon heating. Heating whey protein concentrates in the presence of lactose not only affected lysine, but also impaired enzymic liberation of other amino acids, according to the severity of heat treatments and aW.     

Thermal Effects on in vitro Protein Quality of Red Kidney Bean (Phaseolus vulgaris L.)

Significant thermal effects on in vitro protein quality of red kidney beans were observed. Beans autoclaved at 121°for 10 and 20 min, and common home-cooked beans had improved protein quality. Uncooked beans, and those autoclaved at 128°for 20 min and at 121°for 90 min had reduced protein quality compared to canned beans and those autoclaved at 110°for 20 min and at 121°for 40 and 60 min. Amino acid scores, essential amino acid index and available lysine (%), corrected for in vitro protein digestibility gave comparable results in evaluation of protein quality. Specific lysine, methionine, cysteine and other amino acid ratios overestimated protein quality.     

Effect of radiation and other processing methods on protein quality of sunflower meal

The effects of gamma irradiation from a ⁶⁰Co source (10 and 20 kGy), dry heating (121 °C for 10, 20 and 30 min), autoclaving (121 °C at 103.5 kPa for 10, 20 and 30 min) and their combination on chlorogenic acid, soluble protein, available lysine and in-vitro protein digestibility of sunflower meal were studied. The moisture content of the raw sample was 78 g kg⁻¹ as is and on a dry matter basis. The meal contained 26.7 g kg⁻¹ chlorogenic acid, 330 g kg⁻¹ crude protein, 78.5% soluble protein and 2.63 g 16 g N⁻¹ available lysine. Digestibility of raw meal was 81.5%. Chlorogenic acid, soluble protein and available lysine of raw meal decreased during dry heating, autoclaving and radiation processing. The digestibility was significantly affected by processing method (P < 0.05), as well as by the time of dry heating and autoclaving. The influence of combination methods revealed that irradiation alone had a little effect on chlorogenic acid and in-vitro protein digestibility. Autoclaving plus irradiation up to 20 kGy markedly improved the digestibility (90%). Therefore, the results suggested that the combination of autoclaving for 10 min plus irradiation up to 20 kGy has a beneficial effect on the protein quality of sunflower meal with little effect on its content of soluble protein, available lysine and markedly reduced chlorogenic acid by 87%, more than other processing methods. © 1999 Society of Chemical Industry     

Nutritional, Microbiological, and Sensory Qualities of a Peanut Beverage Prepared Using Various Processes

Nutritional, microbiological and sensory qualities of peanut beverages processed at 85°C, 100°C and 121°C for 15 min and 121°C for 3 sec were determined. Heating improved the digestibility of peanut beverages, particularly those processed at 121°C for 3 sec and 85°C for 15 min. Methionine was particularly sensitive to the treatment at 121°C. The limiting amino acids were threonine, cystine, valine, lysine and tyrosine. No microbial growth was observed in products processed at 100°C and 121°C followed by storage at 4°C and 30°C for 20 days. Beverage processed at 85°C and stored at 30°C for 3 days contained an aerobic microbial population of 2.4 × 10⁴ CFU/mL. The beany flavor was least pronounced in beverages processed at 100°C for 15 min and strongest at 121°C for 3 sec.     

Availability of essential amino acids from proteins. I. Beef serum albumin

Available essential amino acids from beef serum albumin were determined microbiologically, after total enzymic hydrolysis of the protein by papain, leucine aminopeptidase and prolidase. Samples of pure beef serum albumin of different moisture content were heat-treated with glucose at 90° or without it at 121°. In the enzymic digest of the protein, available essential amino acids were determined using Streptococcus faecalis, S. zymogenes and Lactobacillus arabinosus. The content of essential available amino acids was correlated with the degree of in vitro digestibility of heat-treated albumin. The amount of lysine determined by Carpenter's method with fluordinitrobenzene did not correspond to the values found for lysine by microbiological analysis with S. faecalis. Lysine reactive with fluordinitrobenzene was found in the non-digestible residue of the protein, so that the values obtained by the chemical method are probably higher than the actual amount of available lysine. The results for the trypsin digest of the albumin were similar by both methods. The availability of lysine as well as that of amino acids in general depended on the enzymic digestibility.     

Effect of irradiation and other processing methods on in-vitro digestibility of rapeseed protein

Abstract. Effect of irradiation (1 kGy), autoclaving (121°C at 103.5 kPa for 5, 10, 15, 20, 25 and 30 min), dry heating (121°C for 5, 10, 15, 20, 25, 30 and 60 min), sprouting (36 h) and their combination on in-vitro digestibility of rapeseed protein was studied. Digestibility was significantly affected by processing methods (P < 0.05). Digestibility of untreated rapeseed protein was 85.7%. Irradiation alone and irradiation plus dry heating showed no effect on the digestibility, while irradiation plus autoclaving markedly improved (88.9%) the digestibility. The digestibility was influenced by the time of autoclaving and dry heating. Maximum value for in-vitro digestibility was recorded for 60 min of dry heating (91.8%). Sprouting of rapeseed exhibited a significant decrease (82.8%) in the digestibility.     

Effects of heat processing on the nutritional value of groundnut products. I. Protein quality of groundnut cotyledons for rats

The trypsin inhibitor activity of raw groundnut cotyledons was approximately 20% of that found in raw soyabeans but was apparently sufficient to cause significant pancreatic hypertrophy in rats receiving 15% protein from this source in their diet. Autoclaving at 121° for 0.5 h reduced the inhibitor activity to one-fifth; dry heating for the same time at this temperature reduced it to one-half. There was a tendency for 0.5 h heating, wet or dry, at 100–121° slightly to increase the net protein utilisation (NPU) value of the protein for rats. Dry heating at 121° for 4 h severely reduced NPU; fluorodinitrobenzene-available lysine in the severely heated material was similarly reduced but there was little change in the level of available methionine assessed using Streptococcus zymogenes.     

Protein quality evaluation of Amaranthus wholemeal flours and protein concentrates

Based on the amino acid composition, Amaranthus seed protein is known to be of higher quality than most of the major cereal grains. However, protein quality does not solely depend on amino acid profile but also on its digestibility. In this study we determined amino acid composition and in vitro protein digestibility of wholemeal and isoelectric protein concentrates (IPC) from five Amaranthus genotypes. Factors most likely to influence protein digestibility such as heating and presence of antinutrients were studied. Heating increased protein digestibility in wholemeals but slightly decreased it in IPCs. Trypsin inhibitor level was negatively but weakly correlated to protein digestibility, and the level of polyphenolic compounds was negatively and significantly correlated to protein digestibility. A slight deficiency in leucine was noted for wholemeals and in lysine for IPCs. However, based on both in vitro digestibility and amino acid profile, Amaranthus proteins were confirmed to be of better quality than those of other cereals. © 1998 SCI.     

Digestive utilisation of protein and amino acids from raw and heated lentils by growing rats

The effect of autoclave treatment on the digestive utilisation of protein and amino acids from lentils was studied in growing rats. Twenty 3‐week‐old Wistar rats (mean live weight 59 ± 4.8 g) were fed two experimental diets (n = 10 rats per diet) consisting of raw lentils (Lens culinaris M, var vulgaris, cv magda‐20) (diet RL) or lentils autoclaved at 120 °C and 1 atm for 30 min (diet AL). An additional group of 10 animals was fed a low‐protein (4%) diet and used to estimate metabolic nitrogen and amino acid excretion. Autoclaving caused a 76% reduction in the levels of trypsin inhibitor activity, but failed to improve the faecal digestive utilisation of protein or total amino acids. Lowest essential amino acid true digestibility in diets RL and AL was found for cysteine (60.2 vs 60.1%) and methionine (68.9 vs 66.6%). The protein digestibility‐corrected amino acid score was 71.2 and 66.4% and the availability of sulphur amino acid‐corrected amino acid score was 57.1 and 52.1% for diets RL and AL respectively. Sulphur amino acids were the first limiting ones. Overall, autoclave treatment did not improve protein or total amino acid digestibility from lentils, but caused a significant improvement in leucine and lysine digestibility and a significant decrease in the digestive utilisation of tyrosine and methionine. © 2002 Society of Chemical Industry     

Lysine in cassava based diets: I. A note on the effect of heat on digestibility and available lysine

Heating Conophor seeds and Amaranthus leaf protein concentrate (LPC) for 24 h at 121°C reduced the digestibility of their crude protein contents.Loss in available lysine was moderate in LPC alone and cassava-LPC mixtures heated for 24 h at 121°C (≤45% loss) but high in Conophor seeds and glucose-LPC mixtures (72 and 80% loss respectively).     

Nutritional Evaluation of the Protein in Oilseed Products Heated with Sugars

Defatted flours and protein isolates from glandless cottonseed, peanut, and soybean were complexed with glucose or sucrose in a ratio of 1:1 by weight and heated at 100°C for 0, 2, or 6 hr. Quality changes by the heat treatment were assessed by determining the extent of browning (browning index), in-vitro protein digestibility, available lysine total amino acids, and computed protein efficiency ratio (C-PER). Whereas the sucrose-containing complexes changed very little in all the quality parameters determined, the counterparts containing glucose decreased substantially in protein quality along with the increased intensity of browning. Before heating, protein digestibility of the complex containing defatted flour of an oilseed was lower than that of the isolate counterpart. When heated, however, the isolate-glucose complexes decreased more in protein digestibility than the flour-glucose complexes. The available lysine content decreased by 76-83% for the complexes with glucose in contrast with 2-10% for those with sucrose. As to total amino acids, marked losses in arginine, lysine, tryptophan, and histidine were found in the complexes containing glucose, with the arginine loss as high as the lysine loss. Lysine-rich soy proteins lost lysine in greater percentages than lysine-poor peanut and cottonseed proteins. C-PER decreased by 63-86% in the glucose-containing complexes, with the highest decrease shown for soy flour-glucose. In-vitro protein digestibility, available lysine, and C-PER were all highly correlated (P < 0.01) with browning index. Available lysine was also highly correlated with C-PER.     

The effects of hydrothermal processing on antinutrients, protein and starch digestibility of food legumes

The effects of hydrothermal processing on antinutrients and the protein and starch digestibility of black grams, chick peas, lentils and red and white kidney beans was investigated. The tannins and phytic acid contents in these five food legumes ranged from 770 to 1100 and 970 to 1440 mg/100 g, respectively, whereas protein and starch digestibility of the raw food legumes was found to be from 33.8 to 37.6 and 36.8 to 42.0%, respectively. A reduction in the level of these antinutrients, along with an improvement in protein and starch digestibility, was observed after cooking. The tannins and phytic acid contents were reduced by 33.1–45.7 and 28.0–51.6%, respectively, because of the use of different hydrothermal treatments at 100, 121 and 128 °C. Maximum improvement in protein digestibility (95.7–105.1%) and starch digestibility (116.7–137.7%) was observed on cooking at 121 °C for 10 min. However, cooking in boiling water resulted in improvement in protein and starch digestibility of the food legumes by 86.9–93.3 and 84.0–90.4%, respectively.     

Influence of Frozen Storage and Defrosting on the Chemical and Nutritional Quality of Sardine ((Clupea pilchardus)

Studies were carried out on the changes in solubility in SDS+β-mercaptoethanol, the –SH group content, the amino acid and the fatty acid compositions, and nutritional quality of the muscle protein following freezing, storage at −20°C and conventional defrosting of sardines ( Clupea pilchardus ). During the processes, 8% of the total SH– group content was lost and there was a slight drop in solubility in SDS+β-mercaptoethanol. The amino acids which dropped to the greatest extent were the S-amino acids, followed by histidine, tyrosine, leucine, lysine and phenylalanin. The C22:6/C16:0 ratio dropped and this was considered to be related to oxidation phenomena. The digestibility of protein, biological value and net protein utilization (NPU) also dropped as a result of the processes studied.     

Effect on protein digestibility of different processing conditions in the production of fish meal and fish feed

The effect of processing conditions on protein digestibility and fluorodinitrobenzene (FDNB)‐reactive (available) lysine in the production of fish meal and extruded fish feed has been studied under pilot and commercial conditions using mink as model animals. Fish meal produced under pilot‐plant conditions at processing temperatures below 70–80 °C (FM1) had protein digestibility of 929 (grams of protein digested per 1000 g protein consumed) compared with 905 when processed at temperatures above 100 °C (FM2). A low‐temperature‐processed commercial fish meal (CFM1) had protein digestibility of 940 compared with 888 for a standard commercial fish meal (CFM2). Pilot‐produced extruded fish feed had protein digestibility of 913 when based on FM1 as the main protein source (95% of total protein) compared with 892 when based on FM2. Commercial extruded fish feed had protein digestibility of 912 when based on CFM1 compared with 871 when based on CFM2. Varying extrusion conditions at the pilot scale, ie temperatures from 100 to 126 °C and moisture contents from 21 to 12%, did not affect protein digestibility. Similarly, under commercial conditions, variation in temperature from 89 to 110 °C and moisture from 24.5 to 19.5% did not affect FDNB‐reactive lysine and protein digestibility. The FDNB‐reactive lysine content and protein digestibility of the extruded feed were less than the values calculated from the ingredient mixture before extrusion. Thus, despite different extrusion conditions not giving different FDNB‐reactive lysine and protein digestibility, the total process, ie extrusion, drying and oil coating, caused a reduction. Copyright © 2003 Society of Chemical Industry     

Nonvolatile taste compounds in cooked Chinese Nanjing duck meat following postproduction heat treatment

Abstract: Taste‐active compounds, including free amino acids, succinic acid and 5′‐nucleotides, and chemical components including moisture, pH, protein, crude fat, and sodium chloride were evaluated in cooked and packaged Chinese Nanjing ducks following heat treatments including control, 99 °C for 40 min, 108 °C for 20 min, 92 °C microwave followed by water heating, 95 °C for 30 min, 121 °C for 25 min. Heat treatment decreased (P < 0.05) the content of Alamine and moisture and reduced the pH value in muscle, but increased (P < 0.05) the protein and 5′‐nucleotides content. The 99 °C group had a significantly lower crude fat content compared with other groups (P < 0.05). The succinic acid content in the control group was significantly higher than in the 121 °C group (P < 0.05). Groups treated at higher temperatures (108 °C, 121 °C, and microwave) had similar equivalent umami concentrations and 5′‐nucleotides, free amino acids content, as well as the derived bitter and sweet taste components compared with the groups treated at lower temperatures. It can be speculated that these differences account for the enhanced flavor of the meat in the 99 °C, 108 °C, 121 °C, and microwave groups compared with the untreated control. Therefore, heat treatment at lower temperature after packaging may prolong product shelf life without any detrimental effects on taste. The results of this study indicate that it is important to use lower temperatures in this type of food processing. However, it may be possible to modify the primary processing steps to improve the content of umami‐like taste compounds such as 5′‐nucleotides. Practical Application: Heat treatment of packaged products is an effective method for eradication of microbes, therefore increasing the shelf‐life. However, such treatment can result in major changes in the sensory perception of meat products, particularly the formation of off‐flavors. This study investigated changes in taste‐active compounds in duck meat following a number of types of heat treatment.     

Effect of home and industrial processing on protein quality of baby foods and breakfast cereals.

The effect of home and industrial processing on the protein quality of baby foods and breakfast cereals, commonly consumed in Pakistan, was studied. The nutritive value of baby foods and breakfast cereals was determined chemically (including amino acid analyses) and biologically in N-balance experiments with growing rats. Lysine and threonine were found to be the limiting amino acids in home and industrially produced baby foods whereas lysine was the limiting amino acid in all the breakfast cereals. The lysine contents of home-prepared baby foods were damaged to a great extent at 150–160°C compared with 100–110°C. The levels of lysine (35–76%) and arginine (10–41%) were in all the breakfast cereals reduced by the industrial processing. The net protein utilisation (NPU) of home-prepared baby foods ranged from 51–81% as compared to 57–60% for industrially produced baby foods. The net dietary protein calorie per cent (NDp cal%) of home and industrially produced baby foods varied between 2.6 and 7.3% and between 7.0 and 7.1% respectively. The industrial processing reduced significantly the true digestibility (4–20%), biological value (13–34%) and net protein utilisation (17–41%) of all the breakfast cereals.     

The nutritive value of porcine blood plasma concentrates prepared by ultrafiltration and spray Drying

Concentrated solutions of porcine blood plasma proteins, prepared by centrifugation and ultrafiltration⁴ were spray dried directly at air inlet temperatures of 154, 170.3, 225 and 243.2 °C. Spray dried concentrates contained ca 86–90% protein, ca 2–7% moisture and ca 5% minerals. The overall amino acid composition of the plasma proteins compared favourably with that of FAO whole egg protein.¹² Although the values of essential amino acids generally fell below the egg values, the only serious limitations were in the content of isoleucine (less than half of the egg value). The chemical score (CS) and essential amino acid index (EAAI) were 49.1 and 70.1 respectively. Rats fed on a diet containing plasma concentrate as the sole protein source showed a net weight increase. NPU carcass for plasma protein was 65.8 ± 1.9 compared with a value of 72.1 ± 0.4 for a casein control. An inverse correlation between denaturation status of plasma proteins and spray drying temperature was found. The percent denaturation as measured on pH 4.0 filtrates increased from 8.4% at an air inlet temperature of 154 °C to 48.6% at a temperature of 243.2 °C. A similar inverse relationship was found between the available lysine content of plasma proteins and spray drying temperature. A maximum decrease in percent lysine availability of 16% was found at an air inlet drying temperature of 243.4 °C.     

Amino acid digestibility studies of autoclaved rapeseed meals using an in vitro enzymatic procedure

An investigation of in vitro enzymatic amino acid digestibility of autoclaved rapeseed meals using the enzyme pronase is presented. A correlation coefficient of 0.991 was obtained when comparing in vitro “available” lysine with “Silcock available” lysine. Autoclaving of rapeseed meal for periods of 15, 30, 60, 120 and 180 min at 103 kPa and 120°C caused the following chemical changes. Lysine, methionine and cysteine in vitro digestibilities were markedly decreased as to a lesser extent were the other amino acids. Conversion of methionine to methionine sulphoxide occurred. Deactivation of trypsin inhibitor from 3.8 units of trypsin inhibitor/mg rapeseed for the non-autoclaved meal to zero for the 15 min autoclaved meal was observed. The in vitro enzymatic method described shows considerable promise as a technique to measure amino acid availability.     

The nutritive value of egg by‐products and their potential bactericidal activity: in vitro and in vivo studies

Technical‐grade egg albumen (TA) and whole egg (WE) by‐products are produced in substantial quantities by egg‐breaking facilities across North America. TA and WE products are recovered during processing but are not approved for human consumption. Both products are known to be rich in fat, maternal antibodies, protein and lysozyme, a bactericidal enzyme. The objective of this research was to explore the potential for egg by‐products to be used as a valuable protein, energy and bactericidal supplement in animal nutrition. To improve the nutritive value of TA and WE, spray‐dried samples were heat treated at various temperatures and their digestible protein content was determined in vitro using a pepsin/pancreatin digestion/dialysis system. In addition, enhancement of lysozyme activity towards Gram‐negative bacteria (GNB) by heat or irradiation was examined. Optimal protein digestibility for TA averaged 80% following heat treatment at 105–110 °C for 10 min. In contrast, protein digestibility of spray‐dried TA was only 55%. Heat treatment (100–122 °C) of spray‐dried WE or hot room storage of spray‐dried TA and WE products at 70 °C for up to 14 days had a minimal effect on protein digestibility in vitro. Heat treatment or γ‐irradiation of lysozyme for at least 20 min at 80 °C or 0.5 kGy, respectively, increased antimicrobial activity towards GNB. When compared with either the heat or radiation control treatments, reductions in Escherichia coli and Salmonella enterica serovar Typhimurium populations increased by at least 1 and 0.5 log₁₀, respectively. In contrast, the effect of irradiation (2 kGy) on the antimicrobial activity of spray‐dried TA was less pronounced. In a feeding trial, rats fed spray‐dried TA and spray‐dried TA subjected to either radiation (1.8 kGy) or heat (80 °C, 20 min) treatment exhibited a body weight gain and protein utilisation equal to or higher than the control (casein diet). In contrast, feeding spray‐dried WE or TA and WE previously maintained in a hot room (70 °C) for 3 days had a negative effect on rat growth and protein utilisation. In the case of WE products this was substantiated by poor digestibility of essential amino acids, including lysine, threonine and, to some extent, methionine. When compared with the control treatments, inclusion of heat‐treated or irradiated TA in the rat diets reduced the population of Enterobacteriaceae. Copyright © 2006 Society of Chemical Industry     

Whey Peptide Fractions Obtained with a Two-Step Ultrafiltration Process: Production and Characterization

Whey protein concentrate (WPC) and heat-treated WPC (90°C., pH 2.5, 10 min) were hydrolyzed with trypsin and chymotrypsin in an ultrafiltration reactor (PM 30). The total hydrolyzates were further fractionated (PM1) resulting in mixtures of polypeptides (M.P.) characterized by a high content of peptides larger than 5000 daltons and fractions made up of amino acids and small peptides (A.A.) rich in small components (<2000 daltons). The heat treatment of WPC modified the molecular weight profile of the fractions (M.P. and A.A.) by increasing their content in larger peptides (> 5000 daltons). Suggestions are given for possible food applications for the fractions produced.