The rheological and structural changes in heat induced pastes and gels of lentil starch and lentil protein composites were investigated at various starch to protein ratios. The starch fraction (Is) ...in the mixtures was varied from 0 to 1 and the total solid content was maintained at 25% (w/w). Results showed that the gel strength of the composite gels increased exponentially with the increase in lentil starch fraction. The pasting temperature increased and the paste viscosity decreased with the increase in the lentil protein fraction. The high starch composite gels (Is > 0.5) showed higher elastic (Ga2) and loss (Ga3) moduli at higher temperature (60 degree C) than at lower temperature (10 degree C). The high protein composite gels (Is less than or equal to 0.5) showed higher Ga2 and Ga3 values at lower temperature (10 degree C) than at higher temperature (60 degree C). Segregation of protein-rich domains was observed in the high starch gels (Is > 0.7) whereas low starch composite gels (Is less than or equal to 0.5) appeared more homogeneous. The microstructure of composite gels appeared to be more fragile with larger pore size and thinner wall compared to the microstructure of starch gel. Both non-covalent interactions (hydrophobic and hydrogen bonding) and covalent bonding were found to contribute to the gel structure and firmness of these composite gels. The NaCl concentration increased the paste viscosity and gel firmness of the composite gels up to 0.25 mM above which the magnitudes of these parameters were decreased. Both the paste viscosity and the gel firmness of the composite gels were found to be higher above the isoelectric point of lentil protein and vice versa. From this study, textural properties of the composite gel/paste were found to be strongly affected by the proportion of the starch and protein as well as the extrinsic factors (pH, ionic strength, presence of reducing agents). Therefore, understanding of gelling behaviour of lentil starch and protein in composite gel would be helpful for structure formation of these two biopolymers in mixtures and would help their application in new product development.
Softening is one of the crucial factors causing the deterioration of postharvest fruit quality. In this study, the effects of konjac glucomannan/low-acyl gellan gum/microcapsule of thymol (TKL) ...coating on the storage characteristics, the ultrastructure of cell wall and transcription expression of pectin-related metabolism of blueberries fruits during low-temperature storage were investigated. TKL coating suppressed the expression of pectin-related enzymes disassembly (VaPE2, VaPE3, VaPG3, VaPL2 and Vaβ-Gal2), reduced the activity of cell wall polysaccharide degrading enzymes (PG, PE, PL, β-Gal, α-Man, α-Af, Xth, β-Xyl, Cx, β-Glu), maintained the normal morphological structure and stability of cell wall, and prolonged the shelf life of blueberries fruits. Overall, TKL is a promising coating that can effectively maintain the firmness, inhibit the postharvest softening and prolong the shelf life of the blueberries during storage period.
•The TKL treatment delayed the quality deterioration of postharvest blueberries.•The enzyme activities of cell wall disassembly were effectively prevented by TKL coating.•The TKL coating suppressed the expression levels of pectin-related genes.•The molecular degradation of WSP and NSP was inhibited according to the TKL treatment.
•The firmness of apple Gala cultivar during storage at different temperature was investigated using acoustic and vibration response.•Four new combined firmness indices Fsum, Fdif, FIsum, FIdif were ...introduced based on dominant frequencies to determine apple firmness.•The two indices FIsum and FIdif had the highest correlation with the reference index (puncture firmness) for the samples kept at 20 °C.
In this research, firmness of Royal Gala cultivar apples during shelf life storage period was measured using acoustic vibration response method. Newly-picked apples were kept in two conditions of temperature and humidity (0 °C, 95 % and 20 °C, 40 % relative humidity). Ten apples from each group were tested every week during storage. Meanwhile, the volume, mass, density and the elasticity modulus of apples were calculated. Tests of acoustic vibration response firmness, puncture firmness and pressure were performed on each sample. The acoustic test was conducted as a nondestructive test with two sensors including a microphone to receive sound signals and a contact accelerometer to receive vibration signals. The puncture test was used as a reference evaluation. The dominant frequencies of sound (FS) and vibration (FV) were obtained and firmness indices (FIS, FIV) were calculated using the formula FI = f2 m2/3. Four new indices Fsum, Fdif, FIsum and FIdif were also calculated. Correlation coefficients of all those for indices were calculated for both groups with the puncture firmness (PF). The highest correlation in the first group belonged to FIS, FIV (98.57 %, 97.40 %) and in the second group belonged to FIsum, FIdif (96.78 %, 96.71 %). Results showed that these new indices were good indicators for determining of apple firmness. Furthermore, results revealed that acoustic vibration response is a promising technique as an inexpensive and fast way for apple texture measurement.
The texture of apples is paramount for determining fruit quality. This research explored the correlations among firmness determinations from the Sinclair iQ™ Firmness Tester (SiQ™), the Aweta ...Acoustic Firmness Sensor (AFS), and eight measurements from the Mohr Digi-Test-2 (MDT) instrument. Assessments were conducted on a collection of nine apple cultivars (Ambrosia, Aurora Golden Gala™, Honeycrisp, Fuji, Imperial Gala, McIntosh, Pink Lady™, Silken, Salish™), with a broad range of firmness values, in each of two years. Sensory analysis of the apples was conducted using a semi-trained panel (n = 10) to evaluate crispness, hardness, juiciness and skin toughness, in quadruplicate at two testing dates, providing eight data points per cultivar per year. Inter-correlations of the instrumental firmness determinations (SiQ™, AFS, MDT) revealed that most values were highly correlated with one another (r > 0.500 n = 72). This suggested that the instruments were tracking similar, but not identical, underlying characteristics. Multiple regression models were developed using the 2016 data to predict the sensory attributes from the instrumental and compositional (titratable acidity, soluble solids concentration, absorbed juice) analyses. Models with the highest R2 were cross-validated using the 2015 data. Accuracy of these models was evaluated using R2 and prediction standard errors (PSEs) - an index quantifying the difference between the predicted and actual values. In general, simple 1- and 2-variable models satisfactorily predicted hardness and crispness, with the R2 values ranging between 85 and 89%, while more complex non-linear models were required to predict juiciness and skin toughness. Correlations coefficients reported in this research allow for interconversion of experimental firmness data, as determined by the SiQ™, AFS and MDT. Regression models predicting hardness, crispness and juiciness from instrumental/compositional analyses, revealed that the quality factor (QF) variable was particularly important for estimation of textural characteristics. Therefore the MDT, among the instruments evaluated, was the instrument of choice for quality assessment of apples. Since cross-validation of the models accounted for a high proportion of the variance (70–82%) in a new data set with small PSEs (2.67–6.36) (on a 100-unit scale), the developed models were appropriate for estimating the apple textural attributes.
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•Firmness values were correlated among three commercially-available instruments.•Simple 1- and 2-variable models predicted hardness and crispness.•More complex models were required to predict juiciness and skin toughness.•Models explained a high proportion of variance and had small standard errors.
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•DEA excitation technique is applied to a vibration experiment for pear fruit.•Pear fruit firmness during storage is evaluated using a firmness index.•Variations of firmness indices ...are approximated based on the least square method.•Mode shapes of pear fruit are extracted via experimental modal analysis.•Evaluating firmness indices demonstrates the effectiveness of the proposed method.
This study proposes a vibration technique based on the dielectric elastomer actuator (DEA) excitation to determine the resonance frequency of La France pear fruit. Postharvest pear fruit ripen during storage to improve their quality. A non-destructive measurement technique is necessary to predict maturity without damaging the fruit. The maturity of pear fruit is correlated with firmness, which can be assessed by a firmness index derived from the resonance frequency and the mass. Because DEAs exhibit characteristics that are conducive to vibration applications such as flexibility, lightweight, responsiveness, and deformability, they can be applied and effectively transfer excitation forces to fruit or vegetables with curved surfaces. In this study, the proposed technique is used to evaluate the variations in firmness indices of pear fruit during storage. Additionally, the firmness is measured using a penetrometer to verify the correlation with the firmness index. Using a vibration test system, the distinct frequency responses of pear fruit are obtained and the resonance peaks of the first elastic mode are observed around 700 Hz. The firmness indices of the target fruit are (21.6±2.5)×106 Hz2 g2/3 on day 0 and tend to decrease during storage. The tendency of each fruit is approximated based on a nonlinear least square method. Moreover, the firmness indices are well correlated with the results of the penetrometer test, demonstrating the effectiveness of the proposed technique to evaluate pear fruit quality.
Fruit firmness is of vital importance in various links of the fruit supply chain, such as determining harvest time, choosing packaging and transportation methods, regulating storage conditions and ...predicting shelf life. Portable devices are useful tools to perform on-site measurements of fruit firmness to guide production, optimize processing procedures, improve handling practices and formulate supply strategies. This paper reviews the recent advances in the design and development of portable devices to evaluate fruit firmness based on sensing mechanical, sonic, vibrational and optical properties of fruits. The principle, structure, composition, application and performance of different portable devices are presented. Since each sensor has its merits and limitations, the integration of multiple microsensors to develop a miniaturized, low-cost and facile-operation device may achieve higher sensing performance in determining fruit firmness.
•Multi-cultivar models were developed using European pear from five cultivars.•A hybrid method eliminated signal variations caused by different pear cultivars.•Pear’s quality indices were predicted ...on-site by a portable Vis–NIR spectrometer.•Model parameters were determined by F values.•Root mean square errors of prediction for SSC and firmness were 0.45% and 8.11N.
The feasibility of a multi-cultivar model’s development for the on-site determination of the internal qualities of European pear (Pyrus communis L.) cv. ‘Abate’, ‘Cascade’, ‘Conference’, ‘Red Comice’ and ‘Wujiuxiang’ was investigated. In total, 240 pear samples, 48 for each cultivar, were collected during fruit post-ripening period under retail stage conditions to explore the performance of a technique for developing soluble solid content and firmness models with partial least squares (PLS) and multiple linear regression (MLR) methods A commercially available portable visible and near-infrared spectrometer was used to collect the absorbance spectra (500–1010nm) of pears. A hybrid method, orthogonal signal correction (OSC) combined with other spectral pre-process methods, such as standardization, second-order derivation and Savitzkye–Golay smoothing, was employed to filter out the variations in signals caused by different pear cultivars. Compared with the routine PLS and MLR models, the performances of the OSC–PLS and OSC–MLR models resulted in higher ratios of prediction to deviation. A new external sample set obtained at the retail stage was used to assess the performances of the best multi-cultivar models of soluble solid content and firmness, which resulted in greater coefficients of determination for prediction of 0.87 and 0.66, respectively, and lower root mean square errors of prediction of 0.45% and 8.11N, respectively. The results highlighted the potential of portable Vis–NIR instruments for the on-site testing of internal quality indices of European pears. The development of a multi-cultivar model for fruit is necessary and significant, in particular for improving the performance of the firmness model.
•The optical properties of ‘Royal Gala’ apples from 400 to 1050nm are presented.•Acoustic firmness was not related to reduced scattering or absorption.•The reduced scattering coefficient increased as ...fruit softened (penetrometer).•Carotenoid and chlorophyll absorption peaks correlated with penetrometer firmness.•The IAD technique is suitable for measuring apple tissue optical properties.
Absorption and reduced scattering coefficients were measured between 400 and 1050nm for ‘Royal Gala’ apples using the inverse adding-doubling technique. Relationships between penetrometer, acoustic firmness and the optical properties are identified. Carotenoid (400–500nm), and to a lesser extent chlorophyll-a (680nm), absorptions were found to correlate with penetrometer firmness, with correlation coefficients equal to −0.69 and 0.52 respectively. The reduced scattering coefficient across all wavelengths increased as fruit softened. An average correlation coefficient of −0.68 was found between the reduced scattering coefficient (550–900nm) and penetrometer firmness. No correlation was found between the AWETA acoustic firmness and either of the optical properties. A correction was developed to improve the correlation between penetrometer firmness and carotenoid absorption. This compensated for errors introduced by light loss in the inverse adding-doubling system and improved the correlation from −0.68 to −0.78.
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