Changes in texture qualities and pectin characteristics of fermented minced pepper during natural and inoculated fermentation process

Texture qualities and pectin characteristics in fermented minced pepper (FMP) prepared by natural fermentation (NF) and inoculated fermentation (IF) were analysed during fermentation. The results showed variation in texture qualities and pectin characteristics was similar during NF and IF process. The hardness, cell wall material, sodium carbonate-soluble pectin (SSP) and chelate-soluble pectin (CSP) content, and CSP esterification degree decreased, while water-soluble pectin (WSP) content significantly (P < 0.05) increased after fermentation. The rhamnose (Rha) molar ratio in three pectins increased, but arabinose (Ara) and galactose (Gal) molar ratios in most pectins decreased after fermentation. Changes in Ara/Gal and (Gal + Ara)/Rha ratios represented the backbone and branched chains of rhamnogalacturonan-I in three pectins depolymerised during fermentation. The decrease of molecular weight (M_w) in CSP was more obvious than that in WSP and SSP, and it was extensively depolymerised into low-M_w pectin after fermentation. Pearson's correlation analysis showed FMP hardness was extremely (P < 0.01) positively correlated with CSP content and significantly (P < 0.05) positively correlated with SSP content and CSP M_w. Hence, CSP was the main pectin to affect texture compared with WSP and SSP, and its characteristics played a crucial role for regulating FMP texture during NF and IF process.     

Preprocessing Ice Storage Effects on Functional Properties of Fish Mince Protein

Holding in ice before mincing and freezing pink perch, Nemipterus japonicus, resulted in significant differences in protein solubility (PS), emulsifying capacity (EC), water binding capacity (WBC), cook loss, thaw drip and texture scores. Functional properties correlated with protein solubility. Significant variations in PS, EC, WBC, texture scores, and thaw drip values during frozen storage suggested these properties may be valuable indicators for determining alterations in functional characteristics of fish proteins.     

Impact of Thermal and Chemical Pretreatments on Physicochemical,Rheological, and Functional Properties of Sweet Potato (Ipomea batatas Lam) Flour

The impact of thermal and chemical pretreatments on the physicochemical, rheological, and functional properties of sweet potato flour was investigated. The chemical pretreatment consisted in dipping peeled sweet potatoes in 1 % (w/v) calcium chloride (CaCl₂), while the thermal pretreatment was achieved by blanching them in tap water at 90 °C for 1 min. Composition in flour moisture, protein, fat, non-reducing sugars, and starch was determined using standard methods. Particle size, color, gelatinization, and rheological properties were analyzed. The water absorption index (WAI) and water solubility index (WSI), as well as the swelling capacity (SC) and sorption isotherms, were determined. The reducing sugar content of sweet potato flour was slightly higher in CaCl₂-pretreated (SSPCaCl₂) samples than that in blanched (SSPB) and control (SSP) samples. However, the lightness of the SSPB sample was lower than that of the SSPCaCl₂ and SSP samples. SSPCaCl₂ sample had the higher value of enthalpy of gelatinization and elasticity modulus G′. The SC was higher in blanched samples. A slight increase in the constant of water binding energy (C _BET) was observed after the CaCl₂ treatment and a marked increase for the blanched sample. Owing to the differences induced by blanching and CaCl₂ pretreatments, CaCl₂-pretreated flour samples are more suitable for bread-making processes and can also be used in food formulations.     

Changes in firmness,cell wall composition and cell wall hydrolases of grapes stored in high oxygen atmospheres

To investigate the effects of high oxygen (O₂) atmospheres on the firmness of ‘Kyoho’ grapes (Vitis vinifera L. X V. labrusca L.), changes in cell wall constituents and hydrolase activities were examined during 60 days of controlled atmosphere storage in air (control), 40% O₂ + 30% CO₂ or 80% O₂ (high O₂) at 0 °C and 95% relative humidity. Grapes stored in high O₂ retained greater firmness than grapes stored in air. The cell wall contents of high O₂-stored fruits contained less water-soluble pectin (WSP), more Na₂CO₃ soluble pectin (SSP) and higher hemicelluloses than air-stored fruits. The levels of cellulose and CDTA-soluble pectin (CSP) did not significantly change. The effects of high O₂ on enzyme activity were dramatic for polygalacturonase and β-galactosidase, moderate for cellulase, and very low for pectinesterase. No pectate lyase was detected. Taken together, WSP, SSP and hemicelluloses appeared to have major structural roles in retaining the firmness and preventing the deterioration of fruits kept in high O₂.     

Moisture adsorption behavior of banana flours (Musa paradisiaca) unmodified and modified by acid‐treatment

The moisture sorption isotherms of untreated banana flour (UBF) and acid treated banana flours (ATBFs) were determined using the static gravimetric method of saturated salt solutions at temperatures of 30°C. The range of water activities (a_w) was calculated to be between 0.14 and 0.97. The equilibrium moisture content absorption data were fitted to four sorption models that differ in the information that can be obtained from each one: Brunauer‐Emmett‐Teller equation (BET), Guggenheim, Anderson and de Boer (GAB), Smith, and Iglesias‐Chirife. Monolayer moisture content (X₀) for UBF and ATBFs were found in the range of 4.06–5.47 (BET model) and 3.87–5.88 (GAB model). The GAB model was found to be the most suitable model to describe the isothermal water sorption of UBF and ATBFs in the intervals proposed of a_w. The X₀ values of both models (BET and GAB) increase with increasing a_w. The Banana flour treated for 11 days (ATBF₃) presents the highest value of X₀ compared with all samples. This result suggests that mechanism of adsorption of water and molecular structure in ATBFs was affected, attributed to changes in morphology and crystallinity of the samples with treatment.     

Process optimisation of encapsulated pandan (Pandanus amaryllifolius) powder using spray‐drying method

A study on the production of spray‐dried pandan (Pandanus amaryllifolius) powder was conducted and optimised using response surface methodology (RSM). Parameters investigated include inlet temperature (170–200 °C) and feed rate (6–12 rpm), with a preset outlet temperature of 90 °C. The estimated regression coefficients (R²) for the physicochemical characteristic and sensory responses of pandan powder were ≥0.800, except for overall acceptability. Some mathematical models could be developed with confidence based on the results from all responses. An optimum drying process for spray drying represents conditions that would yield acceptably high colour index (such as L value, a value and b value), low moisture content, low water activity (a_w), high solubility and high colour, flavour, odour and overall acceptability for sensory responses. Optimum conditions of 170 °C inlet temperature and 6 rpm feed rate, with a constant outlet temperature of 90 °C, were established for producing spray‐dried pandan powder as an edible colouring and flavouring powder. Copyright © 2005 Society of Chemical Industry     

ASSESSMENT of A SEMI-EMPIRICAL FOUR PARAMETER GENERAL MODEL FOR SIGMOID MOISTURE SORPTION ISOTHERMS1

Published sigmoid moisture sorption isotherms (0 < a_w < ～ 0.9) were fitted by the four parameter models m = k₁a_wⁿ¹+ k₂a_wⁿ² where m is the moisture contents (dry basis), a_w the water activity and the k and n values are constants (n₁ < 1 and n₂ > 1). Not surprisingly, the model had the same or better fit than the GAB model. In contrast with both the BET and GAB models, the proposed model is not based on the assumption that there exists a well-defined monolayer of absorbed water. At a_w < ～ 0.4 and n₁ > ～ 0.55, however, the model produces a practically linear a_w/[m(1 – a_w)] vs a_w plot, of the kind used to calculate the monolayer moisture with the BET model. The proposed model can be a convenient means to catalog both sigmoid and nonsigmoid isotherms, and used to calculate the equilibrium water activity of dry mixtures with equations solving software.     

Effects of type of packaging material on physicochemical and sensory characteristics of deep‐fat‐fried banana chips

A storage study of deep‐fat‐fried banana chips was carried out for 8 weeks at ambient temperature (27 °C), using four types of packaging material: laminated aluminium foil (LAF), oriented polypropylene (OPP), polypropylene (PP) and low‐density polyethylene (LDPE). The physicochemical and sensory characteristics of the stored banana chips were analysed at weeks 0, 2, 4, 6 and 8. The quality parameters determined were moisture content, water activity (a_w), thiobarbituric acid‐reactive substances (TBARS), texture (breaking force), colour and sensory attributes. The moisture content, a_w, TBARS and breaking force values of all samples increased during storage. The colour also changed during storage, showing higher L and lower a and b values. Samples packed in LAF had the lowest moisture content, a_w, TBARS and breaking force values. The most notable sensory change that occurred during storage was a decrease in crispness. Samples packed in LAF had higher scores than the other three samples, whilst LDPE gave the lowest scores for crispness as well as product colour. There were no significant differences (P > 0.05) in rancid odour among samples packed in OPP, PP and LDPE. However, there were significant differences (P < 0.05) between samples packed in LAF and the other three samples, with LAF giving the lowest rancid odour. © 2002 Society of Chemical Industry     

Ageing-induced solubility loss in milk protein concentrate powder: effect of protein conformational modifications and interactions with water

BACKGROUND: Protein conformational modifications and water‐protein interactions are two major factors believed to induce instability of protein and eventually affect the solubility of milk protein concentrate (MPC) powder. To test these hypotheses, MPC was stored at different water activities (a_w 0.0–0.85) and temperatures (25 and 45 °C) for up to 12 weeks. Samples were examined periodically to determine solubility, change in protein conformation by Fourier transform infrared (FTIR) spectroscopy and water status (interaction of water with the protein molecule/surface) by measuring the transverse relaxation time (T₂) with proton nuclear magnetic resonance (¹H NMR). RESULTS: The solubility of MPC decreased significantly with ageing and this process was enhanced by increasing water activity (a_w) and temperature. Minor changes in protein secondary structure were observed with FTIR which indicated some degree of unfolding of protein molecules. The NMR T₂ results indicated the presence of three distinct populations of water molecules and the proton signal intensity and T₂ values of proton fractions varied with storage condition (humidity) and ageing. CONCLUSION: Results suggest that protein/protein interactions may be initiated by unfolding of protein molecules that eventually affects solubility. Copyright © 2011 Society of Chemical Industry     

Predicting Water Activity from 0.30 to 0.95 of a Multicomponent Food Formulation

The objective was to develop an equation to calculate the a_w of a mixture of known composition at a given moisture content. A simple equation was derived by combining the Smith isotherm with the Lang-Steinberg mass balance: log (1–a_w) = [MW–Σ(a_iw_i)]/Σ(b_iw_i) where M is moisture content of the mixture, W is total dry weight of the mixture, a_i and b_i are Smith isotherm parameters for the individual ingredient, and w_i is the dry weight of the ingredient. For comparison of experimental and calculated a_w values, an experimental value was used to calculate M from the mixture isotherm and this M was used to calculate a_w, from the model. Four binary and one ternary mixtures of two macromolecules, two solutes and one complex ingredient were included. Twenty-one comparisons between calculated and experimental a_w, over a_w 0.30–0.95 resulted in a maximum error of only 1.86% and a mean error of -0.25%, showing excellent agreement. Only one constraint was found; when the mixture contains i solute (sugar or salt) and the a_w, is below the a_w of saturation for that solute, that solute is deleted from the summations in the Model.     

The effect of salt and fibre direction on water dynamics,distribution and mobility in pork muscle: A low field NMR study

The effect of salt concentration and fibre orientation on water within the meat matrix was investigated by low-field nuclear magnetic resonance (LF-NMR), water-binding capacity (WBC), diffusion studies and histological analysis. Pork M. longissimus thoracis et lumborum samples were cured with 5.7, 15.3 or 26.3% w/w NaCl at a parallel or perpendicular fibre direction. NMR transverse (T₂) relaxation identified three water components (T_2b, T₂₁ and T₂₂) which all exhibited characteristics correlated to WBC. Results indicated that T_2b increases with increasing NaCl concentration. Increasing intra-myofibrillar water and decreasing extra-myofibrillar water resulted in the highest WBC. Water diffused more quickly into the extra-myofibrillar space in samples cured at a parallel fibre direction. This water remained loosely bound in samples cured with the saturated solution (26.3% w/w NaCl) leading to decreased WBC. This study provides further information on water binding within the meat matrix by applying the results of LF-NMR to traditional water-binding theories.     

Effect of frozen storage on lipids and functional properties of proteins of dressed Indian oil sardine (Sardinella longiceps)

Changes occuring in lipids and functional properties of dressed oil sardine during storage at −20°C (±2°C) were investigated for 12 weeks. Significant (P 0.05) changes were observed in the lipids and functional properties of frozen stored oil sardine meat. The extent of lipid oxidation and hydrolysis was strongly associated with decreased protein solubility (P0.01). Decrease in protein solubility (PS) positively correlated (P0.05) with the decrease in emulsifying capacity (EC), relative viscosity (RV) of soluble protein extracts, water binding capacity and negatively correlated with the cook loss. A positive correlation (P0.001) was established between the PS and the ability of soluble proteins to emulsify and stabilise an emulsion. High positive correlation between SSP & EC (P0.001) and PS & EC (P0.001) revealed that myofibrillar proteins are the main protein that decide the emulsion properties.     

Physicochemical Composition of Dry-Cured Ham Processed under Minimal Aging Time/Temperature Conditions

Effects of ham size, aging time and temperature on the physicochemical composition of trichina-infected dry-cured hams were studied. Five muscle groups from small, medium and large short-cure hams and large bag-cure hams were analyzed for a_w, moisture, NaCl and brine concentration. Semimembranosus/Adductor and Rectus femoris groups from the center had the lowest a_w and moisture, and highest NaCl and brine concentrations compared to Biceps femoris + bottom Gastrocnemius groups from the hock. Aging at 32.2°C resulted in higher moisture and lower NaCl and brine percentages. Bag-cured hams were similar to the short-cure hams at 23.9°C. These results provide a detailed dataset of physicochemical analyses for dry-cured hams by individual muscle groups under minimal curing conditions.     

A model of moisture-induced plasticization of crunchy snacks based on fermi' distribution function

The irregular force-deformation relationships of commerical cheese balls and Zwiebacks at nine levels of water activity in the range 0.11–0.85 were recorded with a computer-interfaced Universal testing machine. They were characterized by two empirical stiffness parameters, the force at 10 and 20% deformation, and two jaggedness measures, the apparent fractal dimension of the normalized force-deformation curve and the mean magnitude of its power spectrum. The plots of all four parameters versus the water activity had a stable region followed by a substantial drop at a characteristic water activity level, of the kind expected when a material undergoes a glass transition. The phenomenon over the entire experimental water activity range, could be described by a model whose mathematical formal is a slightly modified version of Fermi' distribution function that is P(a_w) = P_s/{1 + exp[(a_w — a_wcp)]/b_p} + c_p where P(a_w) is any of the stiffness or jaggedness parameters, P_s and c^p constants whose sum is the magnitude of the parameter when the material is in the dry state (c_p is the residual level after plasticization), a_wcp is a characteristic water activity level representing the region where the major textural changes take place, and b_p a constant representing the steepness of the relationship at the transition region.     

Effects of Water-Glycerol and Water-Sorbitol Interactions on the Physical Properties of Konjac Glucomannan Films

Konjac glucomannan (KGM)‐edible films were prepared with different amounts of glycerol or sorbitol as a plasticizer. Films were characterized by moisture sorption isotherm, and following conditioning at different relative humidities, by differential scanning calorimetry and tensile tests. Moisture and polyols (sorbitol and glycerol) were found to plasticize KGM‐based films with respect to their tensile properties. However, thermal properties and water sorption capacity (WSC) of polyolplasticized KGM films were found to vary with water activity (a_w), namely at low a_w (< 0.6), WSC and melting enthalpy were decreased with increasing in polyol content and the opposite was true at higher a_w (>0.6). This was attributed to extensive interactions between plasticizer and KGM that reduced the available active site (‐OH groups) for water adsorption. The presence of polyols at low a_w appeared to suppress crystalline structures due probably to restricted molecular mobility. These effects were diminished when the moisture content was >20%.     

Relationships between various physicochemical,thermal and rheological properties of starches separated from different potato cultivars

Various physicochemical, thermal and rheological properties of starches separated from Indian potato cultivars were related to each other using the Pearson correlation. Amylose content, water‐binding capacity (WBC), swelling power, solubility, ash content, transmittance, syneresis and consistency coefficient (K) were determined. Amylose content was significantly correlated with swelling power (r = 0.904), transmittance (r = 0.656) and syneresis (r = 0.777) of the starches. Thermal properties such as transition temperatures (T_o, T_p and T_c), gelatinisation range (R), gelatinisation enthalpy (ΔH_gel) and peak height index (PHI) of the starches were measured using differential scanning calorimetry (DSC). T_o, T_p and T_c were positively correlated with swelling power and negatively correlated with solubility and WBC. PHI was positively correlated with WBC and negatively correlated with ash content and swelling power. R had a negative correlation with WBC (r = ?0.726) and PHI (r = ?0.737). A positive correlation between R and T_c was observed. WBC was negatively correlated with swelling power (r = ?0.749). Syneresis of potato starches was positively correlated with transmittance, ash content, swelling power and amylose content. K was positively correlated with amylose content (r = 0.587). The results showed a significant variation in various functional and thermal properties of starches separated from different potato cultivars. Copyright © 2004 Society of Chemical Industry     

Relationship of Water Content to Textural Characteristics, Water Activity, and Thermal Conductivity of Some Commercial Sausages

Mechanical properties from cyclic low strain testing, texture profile parameters and thermal conductivity were evaluated for 7 types of commercial sausage products ranging in moisture content from 27.7% to 62.4% and a_w from 0.857 to 0.993. Hardness, fracturability, the apparent moduli, stress al 20% compression, mechanical hysteresis loss, and strain energy all increased with decreasing moisture level, while springiness and the degree of elasticity decreased. Moisture had no significant effect on cohesiveness. A linear relationship was observed between the a_w and the effective mole fraction of water in the brine, the exact nature of which depended on the thermal process which the product had received. Thermal conductivity decreased with decreasing moisture in a linear manner.     

Effect of maltodextrin weight fraction on the amorphous state and critical storage conditions of freeze-dried juices

Diagrams relating to water activity (a_w), equilibrium moisture content (X_w) and glass transition temperature (Tg) are valuable tools for predicting amorphous fruit powders' storage procedure and stability. Thus, T_g–a_w–X_w diagrams were constructed to characterise the amorphous state and define the critical values of water content (X_wc) and water activity (a_wc) of freeze-dried juices of strawberry, pineapple, kiwi and prickly pear prepared with maltodextrin at the dry mass fraction (W_MD) of 0, 0.4 and 0.8. The T_g and sorption data were fitted with a polynomial equation and the Guggenheim–Anderson–de Boer (GAB) model respectively. A Tukey test was performed to evaluate the difference between critical values of the powders (P < 0.05). The a_wc and X_wc increase with W_MD and depend on the chemical composition of the powders. The highest critical values were found in pineapple powders, ranging from 0.174 to 0.632 and 0.029 to 0.142 dry basis (d.b.), and the lowest ones in kiwi juice powders ranging from 0.029 to 0.550 and 0.013 to 0.129 (d.b.). For W_MD of 0.8, however, regardless of juice composition, stable powders in an amorphous state were obtained up to an a_w of 0.52 at 25°C.     

Growth of Staphylococcus aureus as Related to 17O NMR Water Mobility and Water Activity

¹⁷O NMR data were determined for three solute-BHI (Brain Heart Infusion) mixtures. For each solute, NaCl, raffinose and glycerol, NMR data (linewidths and signal intensity) were determined as well as water activity (a_w), moisture contents, and effects on growth of Staphylococcus aureus in media of various moisture contents. Liquid (highly mobile) water content in all media tested was determined by NMR. This mobile water was important and had a stronger correlation with S. aureus growth rate than did a_w or moisture content, although solute effects limited empirical prediction. NMR linewidth also correlated with lag phase.