A chemical basis for sour taste perception of acid solutions and fresh-pack dill pickles

ABSTRACT:  Sour taste is influenced by pH and acids present in foods. It is not currently possible, however, to accurately predict and modify sour taste intensity in foods containing organic acids. The objective of this study was to investigate the roles of protonated (undissociated) organic acid species and hydrogen ions in evoking sour taste. Sour taste intensity increased linearly with hydrogen ion concentration ( R ²= 0.995), and with the concentration of protonated organic acid species at pH 3.5 ( R ²= 0.884), 4.0 ( R ²= 0.929), and 4.5 ( R ²= 0.975). The structures of organic acid molecules did not affect sour taste after adjusting for the effects of protonated organic acid species and hydrogen ions. Sour taste intensity was also linearly related to the total concentration of protonated organic acid species in fresh-pack dill pickles ( R ²= 0.957). This study showed that the sour taste of organic acids was directly related to the number of molecules with at least 1 protonated carboxyl group plus the hydrogen ions in solution. Conclusions from these results are that all protonated organic acids are equally sour on a molar basis, that all protonated species of a given organic acid are equally sour, and that hydrogen ions and protonated organic acids are approximately equal in sour taste on a molar basis. This study provides a new understanding of the chemical species that are able to elicit sour taste and reveals a basis for predicting sour taste intensity in the formulation of acidified foods.     

A Hypothesis for the Chemical Basis for Perception of Sour Taste

ABSTRACT: Sour taste has been considered the simplest of the basic tastes because it is elicited only by hydrogen ions. However, there is not a sufficiently clear understanding of that relationship to allow sour taste intensity to be predicted and rationally modified in foods. On the basis of analysis of sensory data from our laboratory and reanalysis of previously published data, we propose a new hypothesis for the chemical basis for sour taste perception: The intensity of sour taste perception in acid solutions or acidified foods is linearly related to the molar concentration of all organic acid species with at least 1 protonated carboxyl group plus the molar concentration of free hydrogen ions. This hypothesis implies that, on a molar basis, different organic acids will be equally sour, provided at least 1 carboxyl group is protonated. The major effect of pH on sour taste will be to determine the degree of protonation of organic acids. If this hypothesis is confirmed, it will provide a new understanding of the chemical basis for this basic taste perception and have broad usefulness in the formulation of products in which sour taste is an important component of flavor.     

The chemistry and physiology of sour taste--a review

ABSTRACT:  Sour taste is the key element in the flavor profile of food acidulants. Understanding the chemistry and physiology of sour taste is critical for efficient control of flavor in the formulation of acid and acidified foods. After a brief introduction to the main applications of food acidulants, several chemical parameters associated with sour taste are discussed. Special emphasis is given to hydrogen ions, protonated (undissociated) acid species, titratable acidity, anions, molar concentration, and physical and chemical properties of organic acids. This article also presents an overview of the physiology of sour taste and proposed theories for the transduction mechanisms for sour taste. The physiology of sour taste perception remains controversial and significant diversity exists among species with regard to cellular schemes used for detection of stimuli. The variety of mechanisms proposed, even within individual species, highlights the complexity of elucidating sour taste transduction. However, recent evidence suggests that at least one specific sour taste receptor protein has been identified.     

Efficacy of Pressure-Assisted Thermal Processing, in Combination with Organic Acids, against Bacillus amyloliquefaciens Spores Suspended in Deionized Water and Carrot Puree

ABSTRACT:  Effect of organic acids (acetic, citric, and lactic; 100 mM, pH 5) on spore inactivation by pressure-assisted thermal processing (PATP; 700 MPa and 105 °C), high pressure processing (HPP; 700 MPa, 35 °C), and thermal processing (TP; 105 °C, 0.1 MPa) was investigated.  Bacillus amyloliquefaciens  spores were inoculated into sterile organic acid solutions to obtain a final concentration of approximately 1.3 × 10⁸ CFU/mL.  B. amyloliquefaciens  spores were inactivated to undetectable levels with or without organic acids after 3 min PATP holding time. At a shorter PATP treatment time (approximately 2 min), the inactivation was greater when spores were suspended in citric and acetic acids than in lactic acid or deionized water. Presence of organic acids during PATP resulted in 33% to 80% germination in the population of spores that survived the treatment. In contrast to PATP, neither HPP nor TP, for up to 5 min holding time with or without addition of organic acids, was sporicidal. In a separate set of experiments, carrot puree was tested, as a low-acid food matrix, to study spore recovery during extended storage following PATP. Results showed that organic acids were effective in inhibiting spore recovery in treated carrot puree during extended storage (up to 28 d) at 32 °C. In conclusion, addition of some organic acids provided significant lethality enhancement ( P  < 0.05) during PATP treatments and suppressed spore recovery in the treated carrot puree.     

初烤烟叶提取物中酸味关键成分的感官导向分析

为考察烟叶的酸味关键成分,利用凝胶渗透色谱(GPC)分离初烤烟叶的提取物,根据各流份滋味特征评价结果,合并酸味流份,得初烤烟叶提取物的酸味特征组分;建立酸味特征组分中乳酸、乙酰丙酸、苹果酸、富马酸、柠檬酸等5 种有机酸的离子色谱(IC)定量方法;依据定量结果,复配上述5 种有机酸的混合溶液,分别对酸味特征组分溶液和有机酸复配溶液进行滋味稀释分析(TDA);利用三点选配法(3-AFC)测定上述5 种有机酸在水中的味觉阈值,结合其在酸味特征组分中的质量分数,计算各有机酸的滋味活性值(TAV)。结果表明:①酸味特征组分溶液和有机酸复配溶液在TDA实验中表现出一致的最大稀释倍数,证明所考察的5 种有机酸是酸味特征组分中酸味的主要来源。②根据5 种有机酸的TAV推测其对酸味的贡献排序为苹果酸> 乳酸> 乙酰丙酸> 柠檬酸> 富马酸。      

External Concentration of Organic Acid Anions and pH: Key Independent Variables for Studying How Organic Acids Inhibit Growth of Bacteria in Mildly Acidic Foods

ABSTRACT:  Although the mechanisms by which organic acids inhibit growth of bacteria in mildly acidic foods are not fully understood, it is clear that intracellular accumulation of anions is a primary contributor to inhibition of bacterial growth. We hypothesize that intracellular accumulation of anions is driven by 2 factors, external anion concentration and external acidity. This hypothesis follows from basic chemistry principles that heretofore have not been fully applied to studies in the field, and it has led us to develop a novel approach for predicting internal anion concentration by controlling the external concentration of anions and pH. This approach overcomes critical flaws in contemporary experimental design that invariably target concentration of either protonated acid or total acid in the growth media thereby leaving anion concentration to vary depending on the pK_a of the acids involved. Failure to control external concentration of anions has undoubtedly confounded results, and it has likely led to misleading conclusions regarding the antimicrobial action of organic acids. In summary, we advocate an approach for directing internal anion levels by controlling external concentration of anions and pH because it presents an additional opportunity to study the mechanisms by which organic acids inhibit bacterial growth. Knowledge gained from such studies would have important application in the control of important foodborne pathogens such as Listeria monocytogenes , and may also facilitate efforts to promote the survival in foods or beverages of desirable probiotic bacteria.     

杏子酸味烟用香料靶向组分的确定及制备工艺优化

为开发能够改善卷烟感官舒适性的天然酸味烟用香料,采用凝胶渗透色谱（GPC）分离、卷烟感官作用评价、气相色谱质谱联用（GC/MS）等方法确定了杏子粗提物的酸味靶向组分,并以其含量为指标对杏子酸味烟用香料的靶向制备工艺进行了优化。结果表明:①靶向组分为酸味组分,主要由苹果酸、柠檬酸、乳酸、琥珀酸、富马酸、甘油酸和羟基乙酸等7种有机酸组成。②以7种有机酸含量为指标确定了溶剂加热浸提法提取工艺参数:30%乙醇、料液质量比1:5、提取温度75℃、提取时间2.0h;膜分离工艺参数为超滤膜截留分子量8 kD、超滤前料液干物质含量（质量分数）2%（干基计）。③与市售杏子提取物和杏子粗提物相比,采用优化工艺制备的杏子酸味烟用香料中7种有机酸含量最高,对改善卷烟感官舒适性的效果最好。      

Anthocyanin-rich sweet potato lacto-pickle: production, nutritional and proximate composition

Anthocyanin pigment-rich sweet potato (SP) cubes were pickled by lactic fermentation by brining the cut and blanched cubes in common salt (NaCl, 2–10%) solution. They were then inoculated with a strain of Lactobacillus plantarum (MTCC 1407) and incubated for 28 days. Treatment with 8–10% brine solution was found to be organoleptically most acceptable. The final product with 8% and 10% brine solutions had a pH (2.5–2.8), titratable acidity (TA) (1.5–1.7 g kg⁻¹), lactic acid (LA) (1.0–1.3 g kg⁻¹), starch (56–58 g kg⁻¹) and anthocyanin content (390 mg kg⁻¹) on fresh weight basis. Sensory evaluation rated the anthocyanin-rich SP lacto-pickle acceptable based on texture, taste, aroma, flavour and after taste. Principal component analyses reduced the eleven original analytical and proximate variables (pH, TA, LA, starch, total sugar, anthocyanin, organic mater, ash, fat, protein and calories) to three independent components (factors), which accounted for 91% of the total variations.     

Umami Taste Enhancement of MSG/NaCl Mixtures by Subthreshold L-α-Aromatic Amino Acids

l ‐Phenylalanine (l ‐Phe) and l ‐tyrosine (l ‐Tyr) are L‐α‐aromatic amino acids that have recently been discovered to be important components of the savory fractions of soy sauce in addition to l ‐glutamate. Their effects are evaluated on the umami or savory taste of monosodium L‐glutamate (MSG), with or without sodium chloride (NaCl). Because l ‐Phe at subthreshold concentration (1.0 mM) significantly enhances an umami taste of a MSG/NaCl mixture (P= 0.000), combinations of 4 subthreshold concentrations (0, 0.5, 1.5, and 5.0 mM) of l ‐Phe with a weakly suprathreshold MSG (4.0 mM) and NaCl (80 mM) mixture were then rated for salty and umami intensities relative to those of standard solutions. L‐Phe was found to significantly enhance the umami tastes of the MSG/NaCl mixtures when it was added in a concentration range of 0.5 to 5.0 mM (P= 0.000). However, neither the umami taste of MSG alone nor the salty taste of NaCl alone was intensified. In a further experiment, l ‐Tyr at the 3 subthreshold concentrations (0, 0.5, and 1.5 mM) studied was shown to have the same activity as L‐Phe. The phenomenon of umami or savory enhancement by subthreshold aromatic amino acids in the soy sauce system has been established.     

FACTORS AFFECTING THE SODIUM CHLORIDE EXTRACTABILITY OF MUSCLE PROTEINS FROM CHICKEN BREAST, TROUT WHITE AND LOBSTER TAIL MUSCLES

The amount of protein extracted from chicken breast muscle at low salt (0–50 mM NaCl) increased as the salt concentration of the extracting solutions increased. The addition of 10 mM sodium phosphate buffer pH 7 (P_i) caused a marked increase in protein extractability at all salt concentrations. A particular polypeptide chain of about 150,000 daltons appeared to be particularly sensitive to the extraction conditions. At high salt (0.6M NaCl, 50 mM sodium phosphate buffer pH 7.0) a second extraction still contained significant amounts of protein. The amount of protein extracted was maximized at a 1/20 dilution. On the other hand, the protein extract-ability of trout white muscle, showed a smaller P_i effect and very little dependence on low salt concentration. The protein extractability of lobster flexor muscle showed little change with either increased salt or P_i. For all three muscles extraction over time with either high or low salt remained essentially constant after the first day with the most protein being extracted from lobster muscle and the least from chicken muscle.     

基于味觉活力值的烤烟主流烟气关键酸味物质的研究

对51份烟叶样本主流烟气中27种有机酸进行了测定,通过味觉活力值分析技术,鉴定出烟气中的关键酸味物质,以此建立烟气酸味指数模型,并与感官评价进行了比较研究。结果表明:（1）甲酸、乙酸、棕榈酸、琥珀酸、乳酸、苹果酸、油酸、亚油酸和亚麻酸是主流烟气中主要的9种有机酸,异戊酸、辛酸、苯乙酸、苯甲酸、己酸和戊酸在不同样本中含量变化较大,而琥珀酸、乳酸、草酸、苹果酸和肉豆蔻酸的变化较小。（2）甲酸、乙酸、异丁酸、丁酸、异戊酸、戊酸、乳酸和琥珀酸等8种有机酸在51份样本中的味觉活力值即TAV均＞0.1,是烤烟主流烟气中关键的酸味物质,大小排序是异戊酸＞乙酸＞戊酸＞甲酸＞丁酸＞琥珀酸＞异丁酸＞乳酸,其它19种有机酸的贡献率可以忽略不计。（3）以8种关键酸味物质味觉活力值为基础,首次提出并建立的烟气酸味指数模型,在主流烟气酸味强度评价方面与感官评价之间取得了较高的趋势一致性,佐证了关键酸味物质研究的科学性,为卷烟烟气味觉特征剖析和调控技术提供支持。      

Analysis of binary taste-taste interactions of MSG,lactic acid,and NaCl by temporal dominance of sensations

Temporal dominance of sensations (TDS) is a relatively novel sensory evaluation technique that measures the temporal evolution of sensory perception. The sensory properties of food or drink products have been described by TDS; however, basic sensory data on TDS are still lacking. We analyzed TDS data for solutions of three basic tastes (umami, salty, and sour) and their binary combinations. The duration of TDS for the main taste of each type of solution (monosodium glutamate [MSG] for umami, sodium chloride [NaCl] for saltiness, and lactic acid for sourness) increased in a concentration-dependent manner. In addition, the duration of the umami taste of MSG was longer than that of MSG/inosine 5′-monophosphate solution with an umami taste of equivalent intensity. The duration of NaCl saltiness was increased by coexistence with MSG and decreased by coexistence with lactic acid. On the other hand, the duration of the umami taste of MSG was suppressed by coexistence with NaCl but not lactic acid, while the duration of the sour taste of lactic acid was suppressed by MSG but not NaCl. These findings provide novel insight into the temporal sequence of basic taste perception during food consumption.     

Independent effects of acetic acid and pH on survival of Escherichia coli in simulated acidified pickle products

Our objective was to determine the effects of organic acids and pH on the rate at which selected strains of Escherichia coli O157:H7 die in acid solutions representative of acidified pickle products (pH < 4.6). We used gluconic acid/sodium gluconate (pKa = 3.7) as a noninhibitory buffer to maintain pH at selected values in the absence of other organic acids. This was possible because we found that the inhibitory effects of this acid on E. coli strains at pH 3.1 were independent of acid concentration over a range of 2 to 200 mM. By this method, the lethal effects of acetic acid solutions (100 to 400 mM) at selected pH values between 3.1 and 4.1 were compared with the effects of pH alone (as determined using gluconate buffer). We found D-values were two- to fourfold lower with acetic acid compared with the effect of pH alone for simulated pickle brines in this pH range. Glutamic acid, an amino acid that is known to enhance acid resistance in E. coli and is a component of pickle brines, protected the E. coli strains from the specific effects of acetic acid.     

ENZYMATIC CHARACTERISTICS OF ALCOHOL ACETYLTRANSFERASE FROM HANSENIASPORA VALBYENSIS, A NON-SACCHAROMYCES YEAST

Alcohol acetyltransferase (AAT) catalyzing 2-phenylethyl alcohol and acetyl co-enzyme A (acetyl-CoA) to form phenylethyl acetate in Hanseniaspora valbyensis was studied. The enzyme was solubilized from lipid particles using 1% Triton X-100 and then purified by three steps of chromatographic separations with diethylaminoethlyl (DEAE) Sepharose, Sephadex G-75 and Octyl Sepharose, respectively. Its molecular weight was estimated to be about 37 kDa. It was discovered that AAT was most active at pH 7.0 and 30C and was stable between pH 7.0–8.0. But most activity was lost at temperatures above 10C. It was found that AAT was strongly inhibited by heavy metal ions such as Hg ^{2 +}, Zn ^{2 +} and Pb ^{2 +}, slightly stimulated by Mg ^{2 +} and slightly inhibited by ethylenediamine tetraacetic acid (EDTA) and Mn ^{2 +}. The K _m was 12.7 mM for 2-phenylethyl alcohol and 23.2 mM for isoamyl alcohol. Finally, the enzyme was observed to catalyze the esterification of other alcohols with acetyl-CoA, but have preference for 2-phenylethyl alcohol.

PRACTICAL APPLICATIONS

Aroma and flavor are affected by the esters that exist in cider. Alcohol acetyltransferase (AAT) can catalyze the formation of esters. Moreover, Saccharomyces cerevisiae and non- Saccharomyces yeast produce diverse esters with different concentration during fermentation. The influence of non- Saccharomyces yeast on the sensory quality of wine and mixed fermentation using different yeasts have been discussed. So, the purification of AAT from Hanseniaspora valbyensis provides an understanding of the formation of esters in non- Saccharomyces yeast.     

Oxidative stability of brined anchovies (Engraulis encrasicholus) with plant extracts

The effect of brining with plant extracts on the oxidative stability of anchovies was investigated during storage. The brining process was done in 15 g 100 mL⁻¹ of sodium chloride solution with water, and with myrtle, rosemary and nettle extracts. Brined anchovies were stored at 4 ± 1  ° C for 28 days. Brining with plant extracts slowed down the lipid oxidation of anchovies. The highest antioxidant effect was observed in brined anchovies with rosemary and myrtle extracts during storage as indicated by peroxide value (POV), thiobarbituric acid reactive substance and oxidative rancidity (OR) scores. Furthermore, OR scores in brined anchovies were well correlated with thiobarbituric acid reactive substance ( r ² = 0.66, P  < 0.01) and POV ( r ² = 0.87; P  < 0.01). The fatty acid profiles were similar among the brined anchovies with plant extracts. These results suggest that brining with rosemary, myrtle and to a lesser extent, nettle extracts prevents development of oxidation in lipids of anchovies during storage.     

PURIFICATION AND CHARACTERIZATION OF POLYPHENOL OXIDASE FROM POTATO: II. INHIBITION AND CATALYTIC MECHANISM

KCN and ascorbic acid showed competitive inhibition patterns with K_is values of 0.032 and 0.27 mM, respectively. Uncompetitive inhibition patterns were obtained with sodium azide, L-cysteine and NaCl with K_ii values of 3.3 mM, 0.12 mM and 0.3 M, respectively. A noncompetitive inhibition pattern was obtained for thiourea with 0.067 mM for K_is and 0.59 mM for K_ii. Cu₂⁺ increased the activity about 2.5 fold at or above 40 μM and K⁺ decreased the enzyme activity about 33% at 0.4 M. Other metal ions did not have any effects on the activity. Two pK values of 5.8 and 8.0 were obtained from V_max profile and two pK values of 5.9 and 8.1 from V_max/K_m profile. The data suggest that cysteine is likely to be involved in catalysis and histidine in binding. Data from chemical modification show that cysteine was completely inactivated at 1.74 mM o-methylisourea, and histidine and tryptophan were modified at much higher concentrations of diethylpyrocarbonate and N-bromosuccinimide, respectively. It is suggested that the protonated cysteine works as a general base, tryptophan as a substrate binding residue and histidine as a oxygen binding residue.     

Influence of sodium chloride and glucose on the aggregation behavior of heat-denatured ovalbumin investigated with a multiangle laser light scattering technique

ABSTRACT:  The molecular characteristics of ovalbumin aggregates formed by heating with NaCl and glucose were investigated with a multi-angle laser light scattering system. The presence of NaCl and glucose affected the formation and molecular structure of the aggregates. Specifically, glucose increased the denaturation temperature of ovalbumin due to thermal stabilization of the native state of ovalbumin, regardless of the content of added NaCl. The surface hydrophobicity of the aggregates was increased by the addition of NaCl, which induced the denaturation of ovalbumin at a lower temperature. Aggregates with a larger weight-average molar mass ( M_w ) and root mean square radius ( R_g ) formed from heat-denatured ovalbumin with NaCl and glucose. The presence of NaCl during heat denaturation caused the formation of aggregates with a larger M_w (1.9 × 10⁵ and 3.5 × 10⁶ g/mol for 0 and 10 mM NaCl, respectively) and R_g (14.8 and 80.4 nm for 0 and 10 mM NaCl, respectively). Over a certain amount of NaCl, the addition of more glucose resulted in the formation of more aggregates with greater M_w and R_g values. In sum, the thermostability of ovalbumin was affected primarily by glucose, but the molecular characteristics of the soluble aggregates formed by heat denaturation varied primarily with NaCl content.     

淡爽型啤酒酸缺陷原因探讨

探讨淡爽型啤酒产生口味酸缺陷的原因,一方面是有机酸含量偏高（主要是乙酸）引起的“真酸”;另一方面则是受到酒体自身的其他不利影响而带来的“假酸”,如酒体老化、醇酯含量低等。