Effect of the add-back process on the free amino acid pool of potatoes

The major losses in nitrogen and free amino acids (FAA) of the potato during the add-back (A-B) process were in the pre-cooking and mash-mixing steps (Fig. 1). These losses were due to leaching of nitrogen compounds into the processing water and heating. The FAA pool of the potato is composed mainly of the amides (asparagine and glutamine), aspartic and glutamic acids (approx. 53%). These amino acids were degraded substantially during the add-back process. There was also a significant loss in valine, threonine, serine, leucine, phenylalanine, and arginine, but no change in gamma-aminobutyric acid (GABA).     

Impact of enzymatic mash maceration and storage on anthocyanin and color retention of pasteurized strawberry purées

Strawberry purées were prepared using a commercial polygalacturonase (PG) and a highly purified pectinesterase (PE) preparation, respectively. To elucidate the effect of pectin on color stability following enzymatic pulp maceration, pectin composition was studied by isolating and fractionating the alcohol-insoluble residue from the strawberry purées. The purées were stored at +20 and +4 °C in the dark over a period of 24 weeks monitoring the amounts of monomeric and polymeric anthocyanins as well as antioxidant activities (FRAP, TEAC). Individual anthocyanins were analyzed by HPLC–DAD–MS ⁿ , and color measurements were obtained in the CIE L*a*b* system. Pectin composition was significantly modified following enzymatic maceration of the purées. While PG treatment generally resulted in pectin losses, oxalate-soluble pectins were increased in PE-treated purées. After 24 weeks of storage, the best anthocyanin retention was observed in PE-treated purées. Such products also revealed greatest anthocyanin half-life values and lowest proportion of polymeric pigments. Compared to an untreated control, enzymatic purée maceration using the PG was also beneficial for pigment retention, but less effective than PE. In contrast, color and antioxidant activity were independent of both enzymatic treatments. An initial heating step (90 °C, 10 s) for immediate inactivation of native enzymes such as polyphenoloxidases slightly improved pigment stability, while lowered temperature during mash maceration was less effective. However, by far best color and pigment retention were achieved when the purées were stored at 4 °C in the dark.     

Thermal inactivation of strawberry polyphenoloxidase and its impact on anthocyanin and color retention in strawberry (Fragaria x ananassa Duch.) purées

Strawberry (Fragaria x ananassa Duch.) cultivars were screened for their polyphenoloxidase (PPO) activities, and thermal stability of PPO was evaluated in vitro for three cultivars under different time–temperature regimes (60, 75 and 90 °C for 3 and 5 min, respectively). Heating strawberry purées should further elucidate the impact of thermal treatments on strawberry PPO in its natural matrix (‘in situ’ activity). To evaluate the consequences of PPO inactivation on anthocyanin and color stability, the purées were stored for 28 days at +20 °C monitoring the contents of monomeric, polymeric (spectrophotometrically) and individual anthocyanins (HPLC–DAD–MSⁿ) as well as color properties (CIE L*a*b*). Antioxidant activities (FRAP), total phenolic (Folin–Ciocalteu) and ascorbic acid contents of freshly prepared and stored purées, respectively, were determined spectrophotometrically. PPO activities varied considerably among the cultivars investigated. Accordingly, different time–temperature regimes were required for their complete in vitro and in situ inactivation. Unexpectedly, thermal inactivation of PPO was disadvantageous regarding pigment and color retention of strawberry purées, which was ascribed to partial regeneration of PPO. Hence, protection of antioxidants, total phenolics and ascorbic acid from oxidative degradation could not be achieved by heating the purées prior to storage.     

Polyphenol content and antioxidative activity in apple purées with rhubarb juice supplement

The purpose of the present study was to evaluate the effect of rhubarb juice addition and peeling in apple purée production and storage on its phenolic composition, antioxidant activity and colour. The apple material used in this study was of two varieties: Sampion and Idared. The apple purées prepared in three variants (control purées, peeling purées and purées with 5% of rhubarb juice) were stored for 3 and 6 months at 30 °C. Apple purées were investigated for their antioxidant activity, change of colour and contents of phenolic compounds plus the polymer procyanidins and degree of polymerization (DP). The preparation of purées from apples without peeling and the addition of rhubarb juice during purée preparation had significant influence on polyphenol content. The purée prepared from peeled apples of Idared variety had phenolic content 2.2 times lower than the control sample (non‐peeled apples). The highest level of total polyphenols was found in Idared + rhubarb sample (129.82 mg 100 g^?1 purée). The content of this compound in Idared control sample was more than 2.8 times lower than in Idared purées with rhubarb. The use of non‐peeled Idared apples and 5% of rhubarb juice in purée preparation significantly increased polymeric procyanidins from 11.68 to 75.20 mg 100 g^?1 and other phenolics from 9.23 to 54.62 mg/100 g. This effect for Sampion apples was smaller. The procyanidins during purées storage were more stable in samples with rhubarb juice addition. The purée samples with the addition of rhubarb juice had higher antioxidant activity measured using ABTS (2,2′azinobis‐(3‐ethylbenzthiazoline‐6‐sulphonic acid)) than purée samples without the addition (two times higher for Idared variety) of rhubarb juice. After 3 and 6 months of storage at temperature 30 °C, the antioxidant capacity decreased in all purées. Rhubarb juice had only high and positive effect on L* value in the case of Idared variety. The results showed that all Sampion apple purées had higher L* values than Idared.     

In Vitro Digestibility of Thermally Processed Diafiltered Whey as Influenced by Water Activity

Diafiltered whey protein concentrates of varying water activity were heated at 121°C for 83.3 min (5000 s). Nitrogen and amino acid digestibilities were determined by the digestion cell technique. Whey nitrogen digestibility significantly decreased only at a water activity of .97. Although this heat treatment did not affect the amino acid profile of the protein, the relative digestibility of most amino acids was slightly increased at a water activity of .3 but relative digestibility decreased at a water activity of .5 and .97. At a water activity of .7, digestibility slightly increased for aspartic acid, threonine, glutamic acid, proline, cysteine, isoleucine, histidine, and arginine and decreased or remained unchanged for the other amino acids. At a water activity of .97, the relative digestibility of aspartic acid, threonine, serine, glutamic acid, glycine isoleucine, leucine, and phenylalanine, significantly decreased. Water activity plays a role in the structural organization of heated whey, which in turn affects the enzymatic liberation of amino acids.     

Pyroglutamic acid development during grape must cooking

A study of the pyroglutamic acid development during must cooking as glutamine and glutamic acid degradation product was carried out. Pyroglutamic acid was detected in two white musts (Trebbiano toscano and Spergola) and in a red one (Lambrusco) previously cooked by means of a laboratory-scale equipment emulating the real process. Results showed that pyroglutamic acid sharply increased and glutamine quickly disappeared during the first stages of the cooking process, while glutamic acid was almost linearly reduced throughout all the process. A study carried out by heating the model solutions of the single amino acids showed that both of them underwent degradation following the same trend observed in the musts.     

The applied pretreatment (blanching,ascorbic acid) at the manufacture process affects the quality of nectarine purée processed by hydrostatic high pressure

A nectarine purée was manufactured with different pretreatments (thermal blanching or ascorbic acid – AA – addition), and then, the purée was processed by high‐pressure treatment to evaluate the effect of the initial manufacture conditions in the stability of the processed purées. A thermal treatment was also carried out to compare the effect with the high‐pressure processing (HPP). All applied processes were effective to ensure the microbiological safety of the purées. However, the pretreatment (thermal blanching or AA addition) applied during the manufacture affected the final quality of the processed purées. Initially, the AA addition had a protective effect on colour degradation during the manufacture of the purées; however, when these purées were treated by HPP showed less colour stability during storage, lower bioactive compounds content, and antioxidant activity. In contrast, purées with an initial thermal blanching maintained better the quality after HPP and during storage.     

Content of amino acids and the quality of protein in as‐eaten green asparagus (Asparagus officinalis L.) products

The content of amino acids in fresh green spears and in three as‐eaten products was considered, i.e., in fresh asparagus after cooking and in two products obtained from frozen asparagus stored for 12 months at ?20 °C. One of the frozen products was obtained using the traditional method (blanching–freezing–frozen storage) and then cooked. The other was obtained using the modified technology (cooking–freezing–frozen storage); after the storage period the product was defrosted and heated to consumption temperature in a microwave oven. The limiting amino acid of the first order was methionine with cystine, and of the second order leucine. Essential amino acids constituted 40–43% of the total amino acid content. The dominant amino acids were aspartic acid and glutamic acid. The culinary and technological procedures applied brought about a drastic decrease (50–56% in 16 g N) in tyrosine content.     

Utilization of Amide Nitrogenby the Young Rat

SUMMARY: Effects on body nitrogen gains of supplying nonessential nitrogen as glutamic or aspartic acids, as glutamine or asparagine or as wheat were investigated. It was found that nitrogen gains of rats fed diets containing only purified amino acids as the nitrogen source and relatively high levels of amide nitrogen were significantly lower than those of rats fed the same amounts of total nitrogen, all as α-amino nitrogen. However, they were significanty higher than those of rats fed the same amounts of α-amino nitrogen, but no additional amide nitrogen, indicating some effect of amide nitrogen in body nitrogen storage. Rats fed ad libitum consumed more of the glutamine-containing diet than of one containing isonitrogenous amounts of glutamic acid; analysis of covariante indicated that ad libitum-fed rats also utilized the nitrogen of glutamic acid more efficiently than that of glutamine. Addition of enough sodium bicarbonate to neutralize the hydrochlorides of dietary amino acids had no effect on utilization of amide nitrogen. No differences in nitrogen utilization were found between two groups of rats fed different levels of amide nitrogen as wheat.     

Thermal degradation of precursors and formation of flavour compounds during heating of cereal products. Part I. Changes of amino acids and sugars

Extracts from wheat, rye and barley malt have been used as a source for free amino acids and sugars in MAILLARD reaction studies. By means of special GLC techniques we have determined the content of 16 amino acids and 6 sugars during heating under controlled conditions; temperature, time and pH were used as variables. Large differences in the reactivity between the single amino acids were registered. Lysine as well as arginine, glutamic acid and proline decreased in high amounts within 15 min of heating at 120 °C. While glucose, maltose and maltotriose were reduced significantly during the thermic process with fructose an increase with time and temperature up to 120 °C was observed. Extreme pH values below 5 and above 7 caused high losses in amino acids. Increasing pH values supported the formation of fructose during heating.     

Changes in the amino acid compounds of the wholecrop wheat during ensiling and after fermentation

Changes in amino acid fractions of chopped low-to-medium protein whole-crop wheat were studied at four stages of maturation and at two stages after a 24 h wilting period. Tests were carried out after an ensiling period of 90 days, and after a further 7-day post-fermentation aerobic exposure. Total amino acids contents in the dry matter during the fermentation period remained stable. Quantities of essential amino acids decreased during maturation and fermentation and remained stable during post fermentation aerobic exposure. The highest amino acid concentrations recorded in the fresh material were those of arginine, lysine, glutamic acid, alanine, leucine, glycine and aspartic acid. Free amino acids varied from a low level in the fresh material < 10% of the total amino acids to ca 65% after the aerobic process. Ammonia-N content increased in the silage and remained relatively stable on post fermentation aerobic exposure. The concentration of all free amino acids increased except arginine and glutamine during the ensiling period and post fermentation aerobic exposure. After wilting, an increase in free amino acids and a decrease in insoluble amino acids was recorded. The changes in concentration of 18 amino acids during ensilage and following post fermentation aerobic exposure are given.     

Effect of canning and storage on carotenoids (vitamin A activity) and vitamin C in Spanish and Turkish oranges

Canning caused a small reduction in the vitamin C content of orange purée of both Spanish and Turkish varieties; subsequent storage for 24 months at 10°C caused complete loss of vitamin C. Carotenoids, however, were retained to a limited extent after storage and similar amounts were present at both room temperature and at 10°C. Most of the vitamin C in the flavedo was retained after 24 months' storage at - 20°C but there was a considerable fall when the frozen material was thawed and stored at room temperature for 4 days. Thirteen carotenoids were present in both varieties of purée, with three additional ones in the Spanish variety and one additional one in the Turkish variety. Despite the heating in acid conditions involved in the canning process, only two of the pigments, violaxanthin and flavoxanthin, isomerised from the all-trans to cis-trans isomers.     

Growth and germination of proteolytic Clostridium botulinum in vegetable-based media

The growth of proteolytic Clostridium botulinum from spore inocula and changes in spore counts in mushroom, broccoli, and potato purées were monitored. Four strains of proteolytic C. botulinum types A and B were inoculated separately at approximately 10(4) spores per ml in nutrient broth and vegetable purées incubated at 15, 20, and 30 degrees C for up to 52 days. The times for the cell populations to increase 1,000-fold (T1,000) in the tested vegetables (1 to 5 days at 30 degrees C, 3 to 16 days at 20 degrees C, 7 to > 52 days at 15 degrees C) were similar to those for meat or fish. Only temperature significantly influenced growth rate. In contrast, the lag phase depended on the strains and media tested, in addition to temperature. Lag times and T1,000S for proteolytic C. botulinum were longer for potato and broccoli purées than for mushroom purée. These differences were not related to different pHs or redox potentials. The germination level, evaluated as the decrease in the spore count, was low. The addition of a germinant mixture (L-cysteine, L-alanine, and sodium lactate) to some strains inoculated in vegetable purées resulted in an increase in germination, suggesting a lack of germination-triggering agents in the vegetable purées.     

广东河源客家黄酒氨基酸分析

为分析广东客家黄酒关键工艺中的炙酒、贮藏、原料等对客家黄酒氨基酸的组成、含量及呈味特性的影响,采用日立氨基酸自动分析仪分析检测客家黄酒中的氨基酸含量,通过计算氨基酸分值、味道强度值(DoT)等确定各氨基酸对客家黄酒的影响。结果表明,客家娘酒中总氨基酸含量在2658.99mg/L- 5420.632mg/L之间,黑豆娘酒氨基酸含量及总量最高,商品板栗娘酒氨基酸含量最低,客家黄酒中最主要的氨基酸是谷氨酸和天冬氨酸,两者合计占氨基酸总量的20%以上,而胱氨酸、蛋氨酸和苯丙氨酸含量最低,是限制性氨基酸。板栗娘酒氨基酸含量低于传统的糯米娘酒,商品板栗娘酒总氨基酸含量仅为糯米娘酒总氨基酸的49%,必需氨基酸仅为64.69%,脯氨酸和苯丙氨酸含量为糯米娘酒的80%,其余氨基酸仅仅达到50%左右。黑豆娘酒比糯米娘酒总氨基酸含量提高42.6%,必需氨基酸提高23.2%,其中胱氨酸提高1倍,脯氨酸提高92.5%,谷氨酸提高80.7%,甘氨酸和丙氨酸提高40%以上,苏氨酸、丝氨酸、异亮氨酸提高30%以上,天冬氨酸、亮氨酸、酪氨酸提高20%以上。炙酒、贮藏过程能降低氨基酸含量,炙酒后氨基酸总量降低20.3%,炙酒后每一种氨基酸含量都明显降低,其中降低最明显的是蛋氨酸和苯丙氨酸,降低氨基酸含量可达50%,苏氨酸、甘氨酸、胱氨酸、赖氨酸、精氨酸在炙酒过程中降低1/3以上,而亮氨酸、异亮氨酸、组氨酸在炙酒过程中氨基酸降低20%以上;贮藏1年以后氨基酸总量降低12.4%,必需氨基酸降低10.9%,组氨酸和精氨酸降低20%以上,除蛋氨酸和苯丙氨酸以外,其余氨基酸均降低10%以上。计算不同酒样的氨基酸的味道强度即剂量比域因子DoT的排序为Glu ＞ Asp ＞ His ＞ Ala ＞ Lys ＞ Tyr ＞ Ile ＞ Gly,只有谷氨酸(Glu)的DoT 值大于1,说明黄酒中决定口味的氨基酸主要是谷氨酸。本文提出味道指数(Taste Index,TI)作为总体风味的评价指标,其定义为优味氨基酸的味道强度之和与劣味氨基酸的味道强度之和的比值,如果TI > 1,说明风味良好,如果TI<1,则劣味氨基酸占优势,味道不佳。本试验中黄酒的TI指数排序为：商品黑豆娘酒 ＞ 绍兴古越龙山花雕酒 ＞ 商品板栗糯米酒 ＞ 贮藏1年的板栗糯米原酒 ＞ 炙酒后的原酒 ＞ 商品普通糯米酒 ＞ 炙酒前原酒 ＞ 1 。对酒样的氨基酸评价表明,AAS和CS评分排序为炙酒前原酒 > 黑豆商品娘酒> 普通商品糯米酒 > 炙酒后原酒 > 贮藏1年的原酒 > 古越龙山花雕酒 > 商品板栗糯米酒,说明炙酒前酒样和黑豆酒样氨基酸的营养价值较好。     

Ripening time estimation of Kariesh cheese

Kariesh cheese is a popular cheese in Egypt produced by acid coagulation of milk. It can be consumed fresh or after ripening. Proteolysis in cheese was measured by determining soluble nitrogen (SN), amino acid nitrogen (AAN), total amino acids (TAA) and free amino acids (FAA). SN, AAN and FAA increased during ripening. Free amino acids profile revealed in total 16 amino acids and the same distribution of free amino acids. Cheese ripening was influenced by the type of milk and the method of production. The mildly acid sweet flavour was attributed to the concentration of glutamic acid, aspartic acid, proline and valine. Linear regression analysis was carried out to estimate the ripening time of this cheese. A positive correlation between the accumulation of amino acid and ripening time was established. The highest coefficient of determination near one resulted from glutamic acid (R² = 0.99) followed by lysine (R² = 0.97–0.99), then aspartic acid (0.90–0.98). From the linear regression equation for glutamic acid, lysine, aspartic acid or proline, the ripening time of Kariesh cheese in weeks was determined as follows: Time of ripening [weeks] = mg amino acid 100 g cheese-a/b where b = slope and a = intercept of regression straight line at 0 time.     

和田红葡萄汁熬煮过程中游离氨基酸检测与分析

目的研究和田红葡萄汁在熬煮过程中,游离氨基酸含量随糖度升高的变化趋势。方法利用AccQ-Tag-高效液相色谱法对和田红葡萄熬煮汁中游离氨基酸进行定量检测。结果脯氨酸和精氨酸在慕萨莱思中含量最多,其次是赖氨酸、丝氨酸、谷氨酸、丙氨酸、苯丙氨酸,甲硫氨酸含量最少,半胱氨酸未检出。熬煮过程中多数氨基酸含量平稳上升,天冬氨酸和甘氨酸含量略有下降;当糖度达到26°Brix之后,丝氨酸、谷氨酸和甲硫氨酸含量有所下降。结论氨基酸的变化明显受到美拉德反应的影响,总氨基酸的浓缩为慕萨莱思自然发酵及其香味积累提供了前提条件。     

Glutamic acid reactivity in heated protein and protein-alginate mixtures

When heated at 185°C for 35 min, only soya and gluten (out of seven proteins tested) produced measurable quantities of additional water. In the presence of 2% manucol DM (an alginate rich in mannuronic acid residues), the formation of water was markedly increased in the soya and gluten samples but not in the other proteins. Amino acid analysis showed that on heating soya in the presence of manucol DM, the glutamic acid content decreased whilst the aspartic acid content increased. When manugel GMB (an alginate rich in guluronic acid residues) was heated with soya, no loss of glutamic acid was observed and no additional water was formed. Experiments with single acids confirmed that the reaction giving rise to the formation of water primarily involved glutamic acid. The chemical reactivity of glutamic acid with alginates rich in mannuronic acid residues explains the well-established effect of this type of polysaccharide in extrusion processing. In addition, the apparent reactivity of glutamic acid residues in these types of reactions may be a possible reason for the ease with which soya and gluten (proteins rich in glutamic acid residues) can be extruded, while proteins with less of these residues are more difficult to extrude.     

Differentiation of intermediate products (concentrates and purées) from the fruit industry by means of phenolic content

Concentrates and purées are intermediate products in the manufacture of commercial fruit juices. In this paper, the phenolic content [total polyphenols (TP), ortho-diphenols (ORT) and catechins (CAT)] in a large number of concentrates and purées from apple and peach fruits has been determined. The relationships TP/ORT, TP/CAT and ORT/CAT have also been calculated. TP content was found to be significantly higher in the concentrates than in the respective purées whereas CAT content was significantly higher in the purée. ORT was found to be higher in purées than in apple concentrates, but the opposite was observed for peaches. The relationships TP/ORT, TP/CAT and ORT/CAT were higher for the concentrates than for the respective purées. In addition, values for ORT/CAT were higher for the peach products than for the respective apple products. The results show that these phenolic compound measurements enable differentiation between concentrates and purées, as well as between the fruit juices produced from them. The main advantage of measurements of total phenolic compounds is that they are easy to perform in a conventional laboratory, which makes them suitable for routine analysis.     

Reduction of Furan Formation by High-Pressure High-Temperature Treatment of Individual Vegetable Purées

The present study addressed the need for furan mitigation measures at the level of food production, where the effects of extrinsic (process-related) and intrinsic (product-related) properties on furan formation in vegetable-based systems were investigated. For the first time in the literature, the effect of high-pressure high-temperature (HPHT) processing on the formation of furan was demonstrated. HPHT processing was proven to be an interesting alternative for furan reduction in vegetable-based systems, when aiming for sterilization intensities. Following HPHT treatment, the furan concentrations of a wide range of individual vegetable purées dropped to levels close to the analytical limits (1–2 ng/g purée). A higher processing cost might limit the use of HPHT processing to high-value added products, which means that for many other conduction-heated food products, conventional heating would remain the standard technology. As a first step towards control of furan formation in the latter products, a mixed model regression was used to identify the major precursors in vegetable-based systems. Significant correlations were observed for vitamin C and sugars, which were attributed to the efficiency of the conversion and high concentrations, respectively. Next to furan, the HPHT- and thermally treated purées were analyzed for 2- and 3-methylfuran, which are likely to undergo the same metabolic fate as furan. For most of the vegetables tested, the total amount of methylfuran found in the thermally treated purées could not be ignored. Similarly to furan, there was a clear reduction in the concentrations found in the HPHT-treated purées.