Malolactic Activity of Lactic Acid Bacteria during Sauerkraut Fermentation

ABSTRACT: The frequency of lactic acid bacteria (LAB) involved in sauerkraut fermentation with (MDC⁺) or without (MDC^-) the ability to decarboxylate malic acid was determined. The MDC⁺ phenotype was found in > 99% of homofermentative LAB isolated from commercial fermentations. In contrast, heterofermentative LAB isolates from 0.25, 3, 7, and 10 d had only 53%, 54%, 15%, and 11% MDC⁺ phenotype, respectively, indicating that more than 1 strain or species was involved. The malolactic reaction was demonstrated in cabbage juice with known strains of Leuconostoc mesenteroides , raising the question of desirability of such activity in cultures selected for the controlled fermentation of cabbage.     

CHEMICAL AND SENSORY CHARACTERIZATION OF COMMERCIAL SAUERKRAUT1

Canned sauerkraut from eight U.S. companies was analyzed for salt, titra-table acidity (TA), fermentation substrates and end products, volatile sulfur compounds and sensory characteristics. The TA ranged from 0.9–1.5%, while salt content ranged from 1.4–2.0%, which was lower than in previous surveys. High performance liquid chromatography (HPLC) was used to monitor lactic, acetic, malic, succinic, propionic and butyric acids; mannitol, ethanol, propanol, glycerol, glucose, fructose and sucrose. Low concentrations of propionic acid, propanol and glycerol were found. These three compounds are not characteristic of lactic acid fermentations. No butyric acid was detected. GC analysis revealed seven main sulfur compounds (hydrogen sulfide, methanethiol, dimethyl sulfide, carbon disulfide, dimethyl disulfide, allyl isothiocyanate (AITC) and dimethyl trisulfide) and six other organic compounds (methanol, ethanol, n-propanol, 2propanol, acetaldehyde and ethyl acetate) in the headspace of sauerkraut juice. A profile panel characterized aroma, flavor and after-taste of sauerkraut with ten distinct notes. The sour, sulfur and salt notes had the greatest impact on sauerkraut flavor.     

EFFECTS of CONTROLLED ATMOSPHERE ON QUALITY of MINIMALLY PROCESSED APPLE (cv. JONAGORED)

Controlled atmosphere (2% O₂+ 4% to 12% CO₂) storage was found to be advantageous over air storage in terms of overall preservation of fresh-cut apple (cv. Jonagored). After 3 days, CA-stored apple cubes were firmer, showed better color and higher content of fructose and soluble solids content than air-stored cubes. In relation to color preservation this benefit was increased when CO₂ in the atmosphere was increased to 12% CO₂. Controlled atmosphere storage showed no advantage over air storage in relation to sensory evaluation of firmness and flavor.     

Flavor Variability and Flavor Stability of U.S.-Produced Whole Milk Powder

ABSTRACT:  Flavor variability and stability of U.S.-produced whole milk powder (WMP) are important parameters for maximizing quality and global competitiveness of this commodity. This study characterized flavor and flavor stability of domestic WMP. Freshly produced (<1 mo) WMP was collected from 4 U.S. production facilities 5 times over a 1 y period. Each sample was analyzed initially and every 2 mo for sensory profile, volatiles, color, water activity, and moisture through 12 mo storage. Selected volatiles were quantified using solid phase microextraction (SPME) with gas chromatography/mass-spectrometry: dimethyl sulfide, 2-methylbutanal, 3-methylbutanal, hexanal, 2-heptanone, heptanal, 1-octen-3-ol, octanal, 3-octen-2-one, and nonanal. Multiple linear regression with backwards elimination was applied to generate equations to predict grassy and painty flavors based on selected volatiles. All WMP were between 2% and 3% moisture and 0.11 and 0.25 water activity initially. WMP varied in initial flavor profiles with varying levels of cooked, milk fat, and sweet aromatic flavors. During storage, grassy and painty flavors developed while sweet aromatic flavor intensities decreased ( P  < 0.05). Painty and grassy flavors were confirmed by increased levels ( P  < 0.05) of lipid oxidation products such as hexanal, heptanal, and octanal. Hexanal, 2-heptanone, 1-octen-3-ol, and nonanal concentrations were best predictors of grassy flavor ( R ²= 0.38,  P  < 0.0001) while hexanal, 2-methylbutanal, 3-methylbutanal, octanal, and 3-octen-2-one concentrations were best predictors of painty flavor ( R ²= 0.61,  P  < 0.0001). These results provide baseline information to determine specific factors that can be controlled to optimize U.S. WMP flavor and flavor stability.     

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.     

CHARACTERIZATION OF MODEL NITROSYLHEME PIGMENTS WITH VISIBLE, INFRARED AND 15N FOURIER TRANSFORM NUCLEAR MAGNETIC RESONANCE SPECTROSCOPY

Synthetic pigments that model the organic-soluble pigment in heat-processed cured ham were characterized with infrared (IR) and ¹⁵N nuclear magnetic resonance (NMR) spectroscopy. The two pigments synthesized were ¹⁵N nitrosyl (protoporphyrinato- IX) iron (II), or Fe^II PP¹⁵ NO, and ¹⁵N dinitrosyl (protoporphyrinato-IX), or Fe^II PP(¹⁵NO)₂. An NMR spectrum was obtained only for the Fe^II PP¹⁵ NO. The NMR spectrum consisted of a single peak + 1.78 ppm from the Na¹⁵ NO³ and –6.8 from the CH₃NO₂ reference. The IR spectrum included a single NO symmetric stretch at 1801 cm⁻¹. The visible spectrum of Fe^II PPNO did not match the visible spectrum of ham extracts, while it did with FE^II PP(¹⁵NO)₂. An unequivocal structural assignment of Fe^II PP¹⁵ NO was made, but longer NMR runs may be necessary to obtain a spectrum and unequivocal structural assignment of Fe^II PP(¹⁵ NO)₂.     

Hydrophilic and Lipophilic Antioxidant Capacities of Commercial Mediterranean Vegetable Soups (Gazpachos)

ABSTRACT: Gazpacho is a traditional cold Mediterranean soup consisting of 5 vegetables (tomato, cucumber, green pepper, onion, and garlic) and olive oil. Antioxidant activities of commercial gazpachos, processed by different technologies (traditional pasteurized [TP], slight pasteurized [SP], and frozen [F]), were assessed. Both lipophilic and hydrophilic DPPH* radical scavenging capacities (L-RSC and H-RSC, respectively) were determined in terms of EC₅₀ and antiradical efficiency (AE). AE parameter takes into account not only antioxidant concentration but also antioxidant kinetic. L-RSC values were approximately 3-fold lower than the H-RSC values in all the gazpacho soups. Lycopene and total carotenoid concentration showed statistically significant correlation against L-RSC as follows: for lycopene, EC₅₀ (r²= 0.4549, P = 0.0001) and AE (r²= 0.5982, P < 0.0001); for total carotenoid, EC₅₀ (r²= 0.4381, P = 0.0002) and AE (r²= 0.5881, P < 0.0001). In the case of H-RSC, a correlation was found between EC₅₀ values and total phenol content (r²= 0.1570, P = 0.0452) and vitamin C (r²= 0.1751, P = 0.0299). Also, a correlation was found between vitamin C and AE values (r²= 0.3485, P = 0.0012), suggesting a predominant role of vitamin C among others constituents in the kinetic of H-RSC. One serving (200 mL) of TP, SP, or F gazpacho soup corresponds to an intake of 16.4 ± 2.6 mg, 16.3 ± 2.1 mg, or 10.6 0.8 mg of vitamin C equivalents of H-RSC, respectively; and to an intake of 7.0 ± 1.0 mg, 6.9 ± 1.0 mg, or 5.3 ± 0.1 mg of lycopene equivalents of L-RSC, respectively.     

The increase of CO2 permeability of paper packaging with increasing hydration

CO₂ transport through hydrated paper was studied using gas chromatography to measure CO₂ permeability (P) and diffusivity (D). With increasing water content from 0 to 0.8 g water/g paper, P and D increased from 3.47 to 9.03 × 10⁻⁶ m³ m⁻² s⁻¹ bar⁻¹ and from 1.35 to 3.51 × 10⁻⁵ m² s⁻¹, respectively. This resulted from structural changes in the cellulose network as reported in the literature; water sorption isotherms were used to explain these changes using BET theory.     

Effect of Thermal Processing and Carbon Dioxide-assisted High-pressure Processing on Pectinmethylesterase and Chemical Changes in Orange Juice

ABSTRACT: The effects of high-pressure processing (HPP), CO₂-assisted high-pressure processing (HPP + CO₂), and thermal processing on the chemical and physical properties of single-strength Valencia orange juice were evaluated over 4 mo of storage at 4 and 30 °C. The HPP + CO₂ juice had the greatest cloud stability and highest ascorbic acid retention. Volatile compound losses were lowest in the HPP juice and lower in the HPP + CO₂ juice compared to the thermally processed juice (p < 0.05). HPP + CO₂ produced a cloud-stable orange juice with more ascorbic acid and flavor volatiles than thermally processed juice (p < 0.05).     

EFFECT OF ALKALI AND ALKALI-EARTH HALIDES ON TEXTURE AND COOKING YIELD OF COOKED COMMINUTED LEAN PORK

The effects of alkali-and alkali-earth halides and sulfates on the texture and cooking yield of cooked lean comminuted pork were examined. Divalent cations (Ca²⁺ and Mg²⁺) associated with Br⁻, I⁻ and SO^2-₄ imparted a firm texture to meat (peak force values of 17.1–21.1 kg as compared to 8.4 kg for the control sample devoid of any added salt). Peak force values of samples containing monovalent cations were generally low, but for most cases, were higher (P < 0.05) than that of the control. The cooking yields of samples containing divalent cations (regardless of their anion counterparts) were not different (P>0.05) from that of the control. At 200 meq/kg sample, iodides of monovalent cations as well as sodium chloride increased the cooking yield by approximately 5–20% compared to the control.     

The Green Oat Story: Possible Mechanisms of Green Color Formation in Oat Products during Cooking

ABSTRACT:  Consumers occasionally report greenish colors generated in their oat products when cooking in tap water. Here we have investigated pH and ferrous (Fe²⁺) ion as possible mechanisms for this color change. Steel-cut oat groats can turn brown-green color when cooked in alkaline conditions (pHs 9 to 12). Extraction of this color with methanol, and high-pressure liquid chromatography indicated a direct association of this color with the phenolic acid or avenanthramide content of the oat. The presence of 50 mM NaHCO₃ in water will cause oat/water mixtures to turn alkaline when cooked as CO₂ is driven off, generating OH⁻ ion. Although tap water rarely, if ever, contains so much bicarbonate, bicarbonate is used as a leavening agent in baking applications. Industrial interests using baking soda or alkaline conditions during oat processing should be aware of possible off color generation. We have also found that as little as 10 ppm Fe²⁺ will turn oat products gray-green when cooked. The aleurone stained darker than the starchy endosperm. Other divalent cations, such as Ca²⁺ or Mg²⁺ had no effect on cooked oat color. As much as 50 ppm Fe²⁺ may be found in freshly pumped well water, but Fe²⁺ reacts quickly with oxygen and precipitates as Fe(OH)₃. Thus, some freshly pumped well water may turn oats green when cooked, but if the water is left under atmospheric conditions for several hours, no discoloration will appear in the cooked oats.     

Determination of chloride, nitrate and calcium ions in sugar with ion selective-electrodes

Chloride, nitrate, and calcium ion-selective electrodes were tested and found satisfactory for the determination of the corresponding ions in highly refined white sugar, molasses and other impure sugar samples at different stages of sugar manufacturing or refining. The interferences by Br⁻ and I⁻ ions in Cl⁻ determination were eliminated by oxidation with 3 M HNO₃ and passing air to remove the free Br₂ and I₂ formed. The Cl⁻ concentration was then determined with a chloride-selective electrode against a calibration curve. Chloride should not be determined by ashing sugar, since this causes high losses of Cl⁻. It was found that NO₃⁻ and free Ca²⁺ ions could be determined directly in the sugar solution against corresponding calibration curves. Total calcium was determined after ashing of sugar samples. The ash was dissolved in 0.1 M HCl and passed through an anion exchange resin to remove PO³⁻₄ and SiO₂₋₃ ions, and Ca²⁺ was determined as before. Bound calcium was obtained by subtracting values of free from total calcium. Determination of bound calcium was useful to monitor the process of liming. For comparison, the three ions were also determined with acceptable precision without removing interfering ions using the method of standard addition and Gran's plot. The errors of determination for both direct and standard addition techniques were 3% for Cl⁻ and NO⁻₃ and 1–5% for Ca²⁺.     

PURIFICATION AND PROPERTIES OF PHOSPHOLIPASE A2 ISOZYMES FROM PYLORIC CECA OF THE STARFISH (ASTERINA PECTINIFERA)

Phospholipase A₂ isozyme II (PLA₂ II), which showed different mobility on native PAGE from that of the PLA₂ isozyme I (PLA₂ 1) isolated previously, was purified from pyloric ceca of the starfish (Asterina pectinifera). The PLA₂ II mainly released oleic acid from 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine. N-terminal amino acid sequence of the PLA₂ II was SVYQF. Temperature and pH optima of the PLA₂ II were at around 50C and pH 9.0, respectively, and the enzyme activity was enhanced by sodium deoxycholate and 1 mM or higher concentration of Ca²⁺. The PLA₂ II did not show fatty acid specificity for hydrolysis of phosphatidylcholine (PC). Specific activity of the PLA² II was about 10 times higher than that of commercially available porcine pancreatic PLA₂. The PLA₂ II hydrolyzed PC more effectively than phosphatidylethanolamine. These characteristics of the PLA₂ II were the same as those of the PLA₂ I.     

Purification and Characterization of an α-L-Rhamnosidase from Aspergillus terreus of Interest in Winemaking

ABSTRACT: An enzyme with α-L-rhamnosidase activity was purified to homogeneity from a culture filtrate of Aspergillus terreus after growth in a medium containing L-rhamnose as the sole carbon source. The biosynthesis of this enzyme was repressed by glucose. The enzyme had a molecular mass of 96 kDa on sodium dodecyl sulfate-polyacrylamide gel electrophoresis and an isoelectric point of 4.6 as determined by analytical isoelectric focusing. The pH and temperature optima for the enzyme were found to be 4.0 and 44 °C, respectively. Using p-nitrophenyl-α-L-rhamnopyranoside as a substrate, the enzyme exhibited Michaelis-Menten kinetics with K_M and V_max values of 0.17 mM and 84 U/mg, respectively. The enzyme was inhibited competitively by L-rhamnose (K₁ 2.5 mM). Divalent cations such as Ca²⁺ Mg²⁺ Zn²⁺ and Co²⁺ stimulated the a-L-rhamnosidase activity, whereas this was inhibited by Hg2+ and Cd2+. Ethanol (12% v/v) and glucose (21% w/v) decreased enzyme activity by approximately 20%, while this was not affected by SO₂.     

New Kinetic Approach to the Evolution of Polygalacturonase (EC 3.2.1.15) Activity in a Commercial Enzyme Preparation Under Pulsed Electric Fields

ABSTRACT:  The effect of pulsed electric fields (PEF) on polygalacturonase (PG) activity in an aqueous solution of a commercial enzyme preparation was studied. Monopolar square wave pulses of 4 μs were delivered to the solution, which circulated through tubular chambers with 2 stainless steel electrodes in continuous operation. The electric field intensities ( E ) and treatment time ( t ) ranged within 15 to 38 kV cm⁻¹ and 300 to 1100 μs, respectively. Although important reduction of the PG activity could be achieved (up to 76.5% at E = 38 kV cm⁻¹ and t = 1100 μs), the experimental data showed certain enhancement of PG activity under soft conditions (up to 110.9% at E = 15 kV cm⁻¹ and t = 300 μs). A kinetic mechanism involving 2 consecutive irreversible first-order steps was developed to describe and explain the experimental data. The tested model exhibited high accuracy in respect of the experimental data and the error of the model was lower than 4.4%. The kinetic rate constant of the first ( k ₁) and second step ( k ₂), ratio between the activities of intermediate and native forms of the enzyme (Λ), and other quantities related to the model, were obtained within a Bayesian framework. k ₁ resulted independent of the E applied and considerably greater in magnitude order ( k ₁ mean = 6 μs⁻¹) with respect to k ₂, which was dependent on the applied E (mean values ranged from 489E-6 μs⁻¹ at E = 38 kV cm⁻¹ to 1215E-6 μs⁻¹ at 38 kV cm⁻¹). The dependency of k ₂ toward E was described using an exponential relationship.     

基于菠菜品质变化的冰箱冷藏保鲜效果综合评价

本文针对目前家电行业缺乏科学规范的冰箱冷藏保鲜效果评价方法及标准的问题,开展了基于品质多维解析及其衰变规律分析的冰箱冷藏食品保鲜效果评价方法研究。以典型冷藏食品——菠菜为代表,研究了冷藏天数(0、2、4、6、8 d)、冰箱不同储藏层数对冷藏菠菜理化、感官指标的影响。结果表明:失重率(X₁)、总色差(X₂)、叶绿素含量损失率(X₃)和维生素C含量损失率(X₄)体现了菠菜新鲜度的主要理化特性,主成分分析提取出前两个主成分,其贡献率分别为54.694%、29.732%,累计贡献率为84.426%。理化特性的评价公式为:F=0.648×(0.572X₁+0.075X₂+0.559X₃+0.595X₄)+0.352×(0.229X₁+0.883X₂-0.356X₃-0.064X₄)。多元统计分析筛选得出,光泽度(S₁)、硬度(S₂)、生青味(S₃)和总体印象(S₄)可作为菠菜新鲜度感官品质表征的主要指标。感官特性的评价公式为P=(0.352,0.101,0.049,0.498)×(S₁,S₂,S₃,S₄)×(95,85,75,65,30)T。综合理化、感官指标及其权重得出,总新鲜度的评价公式为G=P/F。本文构建了评价冰箱冷藏食品新鲜度的综合评价体系,并进行方法应用验证,为科学评价家用冰箱"实效"提供技术支撑与方法依据。     

Effect of irradiation and modified atmosphere packaging on the microbiological safety of minced pork stored under temperature abuse conditions

The safety of irradiated pork packed in 25% CO₂:75% N₂ and stored at abuse temperature (10 or 15°C) was assessed by inoculation studies involving Salmonella typhimurium, Listeria monocytogenes, Escherichia coli, Yersinia enterocolitica and Clostridium perfringens . Irradiation to a dose of 1.75 kGy reduced pathogen numbers to below the detection limit of 10² cells g^-1. When higher inoculum levels were used (10⁶ cells g^-1) irradiation at 1.75 kGy reduced pathogen numbers by 1 –>5 log₁₀ cycles depending on strain. Clostridium perfringens was the most resistant, and Y. enterocolitica the most sensitive of the pathogens studied.
In all cases when high numbers (10⁶ to 10⁷g^-1) of spoilage and/or pathogenic bacteria were present initially on the pork the meat appeared spoiled, and although irradiation reduced the number of microorganisms, the meat was still unacceptable from a sensory viewpoint after treatment.
It was concluded that the microbiological safety of irradiated, modified atmosphere packaged (MAP) pork is better than that of unirradiated MAP pork.     

Shelf life of Turkish whey cheese (Lor) under modified atmosphere packaging

In this study, the shelf life of Lor cheese stored under different atmosphere compositions was assessed and compared. Lor cheeses were held in four different atmospheres containing: vacuum packaging (VP), 40% CO₂/60% N₂, 60% CO₂/40% N₂ and 70% CO₂/30% N₂ (modified atmosphere packaging). Control cheeses were stored in air. All cheese samples were kept in the refrigerator at 4°C for 45 days and investigated for physicochemical, microbiological and sensory properties. The acidity index value was significantly higher ( P  < 0.05) in the control and vacuum packaged samples than in those stored for the same period under CO₂. Microbiological results showed that modified atmosphere packaging delayed microbial growth compared with air and VP samples. Of the three modified atmospheres, gas mixtures 60% and 70% CO₂ were the most effective for inhibition of growth of micro-organisms. Sensory evaluation (odour and taste) results showed that Lor cheese packaged under modified atmosphere packaging (60% CO₂/40% N₂ and 70% CO₂/30% N₂ ) retained good characteristics for 45 days of storage, while vacuum and control samples were sensorily unacceptable after 10 days of storage.