Apple Firmness Research Articles

Model fusion for prediction of apple firmness using hyperspectral scattering image

Hyperspectral scattering image is an advanced technology widely used in non-destructive measurement of fruit quality. To develop a better prediction model for apple firmness, the present study investigates a model fusion method coupled with wavelength selection algorithms. The current paper first discusses two wavelength selection algorithms, namely, uninformative variable elimination (UVE) and supervised affinity propagation (SAP). The selected effective wavelengths are then set as input to the partial least square (PLS) model. Six hundred “Golden Delicious” apples were analyzed. The first 450 apples were used as sample for the calibration model, whereas the remaining 150 were used for the prediction model. Compared with full wavelengths, the number of effective wavelengths based on the UVE and SAP algorithms decreased to 34% and 35%, but the correlation coefficient of prediction ( Rp) increased from 0.791 to 0.805 and 0.814, whereas the root mean-square error of prediction (RMSEP) decreased from 6.00 to 5.73 and 5.71 N, respectively. A fusion model was then developed using UVE-PLS and SAP-PLS models coupled with backpropagation neural network. A better prediction accuracy was achieved from the fusion model ( Rp = 0.828 and RMSEP = 5.53 N). The model fusion provides an effective modeling method for apple firmness prediction using hyperspectral scattering image technique.

Rheological Characteristics of Apple Skin and Apple Firmness

The modulus and breaking strength of the skins of different apples were measured: McIntosh, Red Delicious, and Empire stored under controlled atmosphere; McIntosh stored at 1.7°C without atmospheric control, and Honey Crisp and Crimson Gala grown under light and heavy crop conditions. The moduli of the skins of Honey Crisp and Crimson Gala were lower (P < 0.05), than those of Empire, McIntosh, and Red Delicious. Peak puncture force values of McIntosh, Red Delicious, and Empire were lower (P < 0.05) than those of Crimson Gala and Honey Crisp; the contribution of the skin of the Honey Crisp apples to the peak force was least among all the studied apples.

Integrated spectral and image analysis of hyperspectral scattering data for prediction of apple fruit firmness and soluble solids content

Spectral scattering is useful for assessing the firmness and soluble solids content (SSC) of apples. In previous research, mean reflectance extracted from the hyperspectral scattering profiles was used for this purpose since the method is simple and fast, and also gives relatively good predictions. The objective of this study was to improve firmness and SSC prediction for ‘Golden Delicious’ (GD), ‘Jonagold’ (JG), and ‘Delicious’ (RD) apples by integration of critical spectral and image features extracted from the hyperspectral scattering images over the wavelength region of 500–1000 nm, using spectral scattering profile and image analysis techniques. Scattering profile analysis was based on mean reflectance method and discrete and continuous wavelet transform decomposition, while image analysis included textural features based on first order statistics, Fourier analysis, co-occurrence matrix and variogram analysis, as well as multi-resolution image features obtained from discrete and continuous wavelet analysis. A total of 294 parameters were extracted by these methods from each apple, which were then selected and combined for predicting fruit firmness and SSC using partial least squares (PLS) method. Prediction models integrating spectral scattering and image characteristics significantly improved firmness and SSC prediction results compared with the mean reflectance method when used alone. The standard errors of prediction (SEP) for GD, JG, and RD apples were reduced by 6.6, 16.1, 13.7% for firmness ( R pred-values of 0.87, 0.95, and 0.84 and the SEPs of 5.9, 7.1, and 8.7 N), and by 11.2, 2.8, and 3.0% for SSC ( R pred-values of 0.88, 0.78, and 0.66 and the SEPs of 0.7, 0.7, and 0.9%), respectively. Hence, integration of spectral and image analysis methods provides an effective means for improving hyperspectral scattering prediction of fruit internal quality.

Preharvest calcium applications inhibit some cell wall-modifying enzyme activities and delay cell wall disassembly at commercial harvest of ‘Fuji Kiku-8′ apples

To improve apple firmness during the postharvest chain, detailed knowledge of the biochemistry underlying ripening-related cell wall disassembly, a very complex event, is required. Apple softening is reportedly mediated by calcium loss from the middle lamella, and accordingly calcium applications are expected to preserve fruit firmness. In this work, pre-harvest calcium sprays (7 weekly applications at 1.6%, w/v, 81–123 days after full bloom) were applied to ‘Fuji Kiku-8′ apples, with the purpose of examining treatment effects on cell wall metabolism during on-tree fruit maturation and ripening. Applied calcium improved cell-to-cell adhesion as indicated by better preservation of the middle lamella and by higher contents of ionically bound pectins in treated fruit, leading to higher fruit firmness levels at commercial harvest. Matrix glycan breakdown was also delayed in response to calcium treatment. Calcium applications partially suppressed pectinmethylesterase, pectate lyase, β-galactosidase, α- l-arabinofuranosidase and β-xylosidase activities, without any apparent relationship with ethylene production rates.

과실 경도측정을 위한 비접촉 초음파 변환기 연구

This study was conducted to develop an non-contact ultrasonic transducer for measurement of fruit firmness. The center frequency of non-contact ultrasonic transducer was 500 kHz. As an active element of non-contact ultrasonic transducer, the 1-3 piezoelectric composite material was selected. That material has high piezoelectric properties such as electro-mechanical coupling factor, <TEX>$k_t$</TEX> and piezoelectric voltage constant, <TEX>$d_{33}$</TEX> and also that material has low acoustical impedance which enables to matching the acoustical impedances between piezoelectric material and air. As a front matching material between 1-3 piezoelectric composite material and air, various kinds of paper with different thickness were tested. To control the dead-zone of the fabricated non-contact ultrasonic transducer, the backing material composed of epoxy resin and tungsten powder were made and evaluated. The fabricated non-contact ultrasonic transducer for fruit showed that the cneter frequency, bandwidth and beamwidth were approximately 480 kHz, 30 % and 12 mm, respectively. It was concluded that non-contact measurement of apple firmness would be possible by using the fabricated non-contact ultrasonic transducer.

Study on Interference from the Peel to Predict Apple Firmness by Near Infrared Spectroscopy

Study on Interference from the Peel to Predict Apple Firmness by Near Infrared Spectroscopy

Optimal Wavelength Selection for Hyperspectral Scattering Prediction of Apple Firmness and Soluble Solids Content

Hyperspectral scattering is a promising technique for nondestructive quality measurement of apple fruit, and extraction of the most useful information from the hyperspectral scattering data is critical for accurate assessment of fruit firmness and soluble solids content (SSC). In this article, a hierarchical evolutionary algorithm (HEA) approach coupled with subspace decomposition and partial least squares regression is proposed to select the optimal wavelengths from hyperspectral scattering profiles of 'Golden Delicious' apples for predicting fruit firmness and SSC. Six hundred apples were tested in the experiment, 400 of which were used for calibration and the remaining 200 apples for validation. Seventeen optimal wavelengths were selected for firmness prediction, which nearly spanned the entire spectral range of 500 to 1000 nm, and 16 optimal wavelengths, all of which were above 600 nm, were selected in the SSC prediction model. The model using the 17 optimal wavelengths for predicting firmness yielded better results (r = 0.857, root mean square error of prediction or RMSEP = 6.2 N) than the full spectrum model (r = 0.848, RMSEP = 6.4 N). For predicting SSC, the model using the 16 optimal wavelengths also yielded better results (r = 0.822, RMSEP = 0.78%) than the full spectrum model (r = 0.802, RMSEP = 0.83%). The HEA approach provided an effective means for optimal wavelength selection and improved the prediction of firmness and SSC in apples compared with the approach using the full spectrum.

Postharvest quality of apple predicted by NIR-spectroscopy: Study of the effect of biological variability on spectra and model performance

The effect of cultivar, season, shelf-life and origin on the accuracy of near infrared (NIR) calibration models for the soluble solids content (SSC) and firmness of apple was studied based on a large spectral data set based on approximately 6000 apple fruit from different cultivars, origins, shelf-life exposure time and seasons. To interpret the variance in the spectra with respect to biological variability, functional analysis of variance (FANOVA) was used. From the FANOVA analysis it was concluded that the effects of cultivar, origin and shelf-life exposure time on the NIR spectra were all significant. The largest differences in the spectra were found around the water absorption peaks (970, 1170 and 1450 nm). External validations using independent data sets showed that the accuracy of the models increased considerably when more variability was included in the calibration data set. In general the RMSEP for predictions of the SSC were in the range 0.6–0.8 °Brix, while for Magness Taylor firmness it was 5.9–8.8 N, depending on the cultivar. It was shown that atypical data can lead to large validation errors. It is, therefore, important to collect a calibration data set which is sufficiently representative for future samples to be analyzed with the developed calibration models and to develop simple procedures for model adaptation during practical use.

Addressing potential sources of variation in several non-destructive techniques for measuring firmness in apples

Measurements of firmness have traditionally been carried out according to the Magness Taylor (MT) procedure; using a texture analyser or penetrometer in reference texture tests. Non-destructive tests like the acoustic impulse response of acoustic firmness sensors (AFSs), a low-mass impact firmness sensor Sinclair International (SIQ-FT) and impact test (Lateral Impact – UPM) have also been used to measure texture and firmness. The objectives of this study were to evaluate the influence of different sources of variation in these three non-destructive tests and to evaluate their respective capabilities of discriminating between fruit maturity at two different harvest dates, turgidity before and after dehydration treatment and ripening after different storage periods. According to our results, fruit studied an unexpected AFS trend with turgidity. Contact measurements (Lateral Impact – UPM and SIQ-FT) appeared highly sensitive to changes in turgidity, but were less able to follow changes in ripening caused by storage period. Contact measurements were suitable for detecting differences between fruits from different harvest dates and showed higher correlation coefficients with reference texture tests than acoustic measurements. The Lateral Impact – UPM test proved better at separating fruits according to turgidity than the SIQ-FT instrument.

Determination of soluble solids and firmness of apples by Vis/NIR transmittance

Firmness and soluble solids content (SSC) of Red Fuji apples were examined by Vis/NIR transmittance to find out factors to be considered in online detection. Four arrangements of light source and fruit-orientation were investigated. The wavelength range of 650–920 nm was selected and two types of data pre-processing were used to enhance the precision of calibration models based on partial least square (PLS). The results show the precision of determination can be improved by using second derivate. The best fruit-orientation was the stem–calyx axis was vertical and the fruit surface was illuminated from the upper side. The precision of determination was enhanced by using multi lamps. According to the high grade of apple to export (SSC ⩾ 14 °Brix, firmness ⩾ 8.0 kg/cm 2), the classifying correctness was 86%. Validation models for SSC and firmness had a r 2 of 0.9532 and 0.8136, as well as, SEP of 0.3838 and 0.5344, respectively.

Relationship between Acoustic Firmness and Magness Taylor Firmness in Royal Gala and Golden Smoothee Apples

This study aimed to evaluate apple firmness measured using both the penetrometer and acoustic methods. The methodologies were applied to Royal Gaya and Golden Smoothee apples (Malus domestica. Borkh) harvested from 12 different orchards in Catalonia (Spain), on six different dates, and over three seasons. The relationship between firmness and physicochemical quality parameters was analyzed at harvest and post-harvest. The results obtained showed a noticeable correlation between Magness Taylor firmness and acoustic measurements in Royal Gala, but no correlation was found for Golden Smoothee. Fruit variety and storage had a clear influence on correlations between the two measurements. Measurements of Magnes Taylor and acoustic firmness seemed to correspond to different physical properties. Acoustic measurements seemed to be a good tool for evaluating changes in tissue firmness during long-term storage, especially for Golden Smoothee apples. The maturity of the fruit seemed to play a more important role in the measurement of Magnes Taylor firmness than in the measurement of acoustic firmness for the Royal Gaya variety.

Detecting chilling injury in Red Delicious apple using hyperspectral imaging and neural networks

Hyperspectral imaging (400–1000 nm) and artificial neural network (ANN) techniques were investigated for the detection of chilling injury in Red Delicious apples. A hyperspectral imaging system was established to acquire and pre-process apple images, as well as to extract apple spectral properties. Feed-forward back-propagation ANN models were developed to select the optimal wavelength(s), classify the apples, and detect firmness changes due to chilling injury. The five optimal wavelengths selected by ANN were 717, 751, 875, 960 and 980 nm. The ANN models were trained, tested, and validated using different groups of fruit in order to evaluate the robustness of the models. With the spectral and spatial responses at the selected five optimal wavelengths, an average classification accuracy of 98.4% was achieved for distinguishing between normal and injured fruit. The correlation coefficients between measured and predicted firmness values were 0.93, 0.91 and 0.92 for the training, testing, and validation sets, respectively. These results show the potential of the proposed techniques for detecting chilling injury and predicting apple firmness.

A Portable Device for the Bioyield Detection to Measure Apple Firmness

The bioyield phenomenon occurs to the apple fruit when it is subjected to compressive loading (i.e., compression or puncture), which causes cell failure without disintegrating the macro tissue structure. Force at the bioyield point is useful for nondestructive evaluation of fruit firmness. A portable device, which consisted of an off-shelf force meter, an actuation driver, and control unit, was developed for detecting bioyield force from apples. Experiments were performed on 'Golden Delicious' and 'Red Delicious' apples to determine the correlation between bioyield force measurement and the standard Magness-Taylor (MT) firmness test, evaluate the sensitivity of bioyield measurement to changes in firmness over time, and quantify firmness variation over the fruit. Bioyield force correlated with MT force with R2 values of 0.835, 0.654, and 0.751 for 'Golden Delicious,' 'Red Delicious,' and the pooled data, respectively. Bioyield force was as sensitive to firmness change over time as MT force (R2 = 0.990) for apples that underwent accelerated softening. The bottom section (the calyx end) of the apple was significantly firmer than the middle and top sections of the fruit. Moreover, the south face or sunny side of the apple was significantly firmer than the north face or shady side of the fruit. Hence, two bioyield measurements should be performed at opposing sides of an apple around the equator to obtain the average firmness value for the fruit. The bioyield device is useful for measuring the firmness of apples in the orchard and during postharvest handling, and for monitoring fruit conditions during storage.

Determination of apple firmness by nondestructive ultrasonic measurement

One of the most important quality indicators for fruit is firmness, which is highly correlated with maturity and storage time. This study was conducted to evaluate the potential use of ultrasonic parameters for the determination of apple firmness. The ultrasonic transmission system consisted of an ultrasonic pulser, two ultrasonic transmitting and receiving transducers specially fabricated for fruit, a digital oscilloscope and personal computer. For firmness of apples, apparent elastic modulus and rupture point were measured from force-deformation curves obtained by a compression test apparatus. Ultrasonic parameters such as ultrasonic velocity, and attenuation were analyzed according to the storage time of the fruit. Correlation analyses among ultrasonic parameters and fruit firmness were performed. A multiple linear regression model describing the relationship between firmness and ultrasonic parameters is proposed. The calibration equations for measurement of apple firmness were developed and validated.

Effects of 1-methylcyclopropene on firmness and flesh browning in Pink LadyTM apples

SummaryPink LadyTM (Malus domestica Borkh. cv. Cripps’ Pink) is an important apple cultivar, which sometimes suffers unacceptable softening after storage and shipping for export. The effects of 1-methylcyclopropene (1-MCP) treatment after harvest on flesh firmness after storage and export were investigated. Fruit were treated with 625 nl l–1 1-MCP for 14 h at 20°C, cold-stored in air for 12 weeks or in a controlled atmosphere (CA; 2.5 kPa O2, 2.0 kPa CO2) for 18 weeks at 0°C, then held in air for 6 weeks at 0°C or 4°C to simulate export shipping. 1-MCP-treated fruit maintained firmness levels 3 – 13 N higher than untreated fruit, after air- or CA-storage and at both shipping temperatures. In actual export experiments, fruit were picked from 12 orchards for CA storage (16 weeks; 0°C) and export (6 weeks; 0°C; air or modified atmosphere) to the UK. The experiments were designed and analysed as four-phase experiments: orchard; treatment (1-MCP); storage; and export. In 2002, 1-MCP-treated apples (625 nl l–1; 24 h; and 20°C) were 16 N firmer than untreated fruit. In 2003, the difference was 7 N. In each year, 1-MCP-treated apples from all 12 orchards met an import standard of 90% of fruit with a minimum firmness of 69 N, whereas the untreated fruit from approx. threequarters of the orchards did not meet this standard. 1-MCP had a greater effect when applied to less mature fruit (i.e., with a lower starch score) in 2002; but, in 2003, the effect was independent of starch score. Flesh browning after storage and export was not affected by 1-MCP treatment, but by orchard and seasonal factors. In conclusion, 1-MCP treatment can facilitate the storage and export of Pink LadyTM apples without unacceptable softening.

Development of a multispectral imaging prototype for real-time detection of apple fruit firmness

Multispectral scattering is a promising nondestructive technique for assessing the firmness of fruit. We report on the development of a laser-based multispectral imaging prototype for real-time detection of apple firmness. The prototype consists of a common aperture multispectral imaging unit, a specially designed multilaser unit, and a fruit handling unit, which simultaneously capture and process four spectral scattering images at a speed up to two fruit per second. The multispectral imaging system is tested for detecting the firmness of Golden Delicious and Red Delicious apples at a rate of one fruit every two seconds. The original 2-D scattering images are corrected by removing noise pixels and incorporating fruit size into the calculations of the scattering distance and intensity. The 1-D scattering profiles are fitted with a four-parameter Lorentzian distribution function. Multilinear regression models are developed using the four Lorentzian parameters for the four wavelengths to predict the firmness of apples. The multispectral imaging system achieves good firmness predictions with the correlation coefficient of 0.86 for both Golden Delicious and Red Delicious. The technique is fast and relatively easy to implement, and has the potential to meet the requirement for online sorting and grading of apples.

Effects of pulsed-vacuum and ultrasound on the osmodehydration kinetics and microstructure of apples (Fuji)

The influence of pulsed-vacuum (PV) and ultrasound on the osmodehydration kinetics and microstructure of apples (Fuji) was investigated. Apple cylinders (15 mm height × 15 mm diameter) immersed in a 60% (w/w) high-fructose corn syrup solution were subjected to shaking (55 rpm), PV (13 MPa vacuum for 5 min + atmospheric pressure for 5 min + same vacuum for 5 min, then atmospheric pressure), or ultrasound treatment (50/60 Hz and 185 W) for 3 h. Changes in water loss, solid gain, and firmness of apples were measured, and the data were fitted using Weibull and Peleg models. In addition, microstructure was observed using scanning electronic microscopy (SEM). The high regression coefficients ( R 2 > 0.96) and low percent mean relative deviations ( E < 6.37%) indicated the acceptability of Weibull model for predicting both water loss and solid gain under all treatments. The Peleg model well described the sample firmness changes with a R 2 ∼ 0.98 and E ∼ 3.24–6.14%. PV resulted in the lowest shape parameter α value (0.74) for solid gain and the greatest rate constant k 1 (40.98 s) for firmness loss, indicating the largest amount of solid gain (3.02%) and the least firmness loss of samples, while ultrasound led to the lowest α value (0.45) for water loss and k 1 value (33.42 s) for firmness loss: the highest water and firmness losses (56.3% and 22.3%, respectively) in samples among three treatments. SEM showed that cell deformation and cell structure collapse were the most severe in ultrasound treated samples, but moderate in PV samples. SEM also revealed a larger amount of solute uptake in the cells of PV and ultrasound treated samples.

WAVELENGTH SELECTION FOR PREDICTING PHYSICOCHEMICAL PROPERTIES OF APPLE FRUIT BASED ON NEAR‐INFRARED SPECTROSCOPY

ABSTRACT Instrumental evaluation tools for fruit quality monitoring are important in the production and postharvest processes as well as in marketing. In the present study, near‐infrared spectroscopy (600–1,100 nm) was applied to study the correlation with fruit soluble solid content (SSC ), fruit flesh firmness and water content of apples (cv. “Fuji”). Genetic algorithm and correlation coefficient (r) method were used to select the most sensitive wavelength combinations, and partial least squares regression analysis was applied to calibrate fruit quality parameter. The validation of models based on the most sensitive wavelengths gave good predictions with an r value of 0.94 and a standard error of cross validation (SECV) of 0.85°Brix for SSC; r = 0.89 and SECV = 7.54 N/cm2 for firmness; and r = 0.96 and SECV = 0.92% for water content. The reduced data set of sensitive wavelengths were found feasible for predicting internal fruit quality.PRACTICAL APPLICATIONSSoluble solid content, firmness and water content are important quality attributes of apples. A nondestructive measurement technique will be valuable for monitoring and sorting apple fruit so that high quality, uniform fresh products can be delivered to the marketplace. In the present study, fruit analyses using the entire near‐infrared fruit spectra or a reduced data set of sensitive wavelengths were compared. The results demonstrate that the selected combinations of sensitive wavelengths were feasible for measuring apple quality properties. The recent research findings provide researchers and instrumentation engineers with information on the performance of different methods to select appropriate wavelengths for reducing the amount of data, e.g., in developing portable or online sensing systems.

Shelf-life extension of fresh-cut “Fuji” apples at different ripeness stages using natural substances

Shelf-life extension of fresh-cut “Fuji” apple at two stages of ripeness (partially ripe and ripe) using natural substances was evaluated. Cylinders of fresh-cut “Fuji” apples were immersed for 1 min in: (a) an aqueous solution of N-acetyl- l-cysteine at 1% (w/v), glutathione at 1% (w/v) and calcium lactate at 1% (w/v) (CGLW), (b) CGLW and d- l-malic acid at 2.5% (w/v) (CGLW + MA) or (c) sterile distilled water (W). Gas production, firmness, color and behavior of native flora (mesophilic bacteria, psychrophilic bacteria, yeasts and mould) were studied weekly over 30 days. Sensory evaluation of fresh-cut apples was carried out at 0 and 15 days during storage. Statistically significant differences ( p < 0.05) were found in ethylene and ethanol production between fresh-cut partially ripe and ripe apples, respectively, reaching values of ethylene of 8.92 and 134.11 μL L −1 and ethanol of 28.73 and 59.39 μL L −1 at 30 days of storage. The firmness of fresh-cut apples was significantly different ( p < 0.05) between partially ripe (initial values of 12.4 ± 0.8 N) and ripe apples (initial values of 8.3 ± 1.0 N), but did not differ throughout the storage time, nor among dipping conditions. An important reduction in lightness ( p < 0.05) was observed throughout storage in the fresh-cut apples with all dipping conditions. However, an influence of the ripeness stage on microbiological stability was not detected. A reduction in growth rate and an increase in the lag phase of mesophilic and psychrophilic bacteria, yeasts and moulds were found in fresh-cut apples dipped in CGLW + MA, which gave as a result an extension of 13 days over the microbiological stability of fresh-cut apples immersed in W (10.1 days). Thus, the use of a combination of CGLW + MA might be a good low cost alternative for the fresh-cut industry since it can offer better maintenance of the physicochemical characteristics and microbiological stability of fresh-cut apples, ensuring a shelf-life of, at least, 14 days.

Nutritional, Sensory, and Physicochemical Properties of Vitamin E- and Mineral-fortified Fresh-cut Apples by Use of Vacuum Impregnation

This study evaluated fresh-cut apples (Fuji) fortified with vitamin E and minerals by use of the vacuum impregnation (VI) technique. A 20% diluted high fructose corn syrup (HFCS) or 1% calcium caseinate (CC) aqueous solution were used as VI solutions, and 0.4% a-tocopherol acetate, 7.5% Gluconal Cal° (GC), and 0.04% zinc lactate (ZL) were incorporated into the VI solutions for the purpose of nutritional fortification. For VI treatment, fresh-cut apples were immersed in VI solutions subjected to vacuum at 100 mm Hg for 15 min following atmospheric restoration for 30 min. Apples were packed in the polyvinyl chloride (PVC) hinged clear containers and stored at 2 °C and 88% RH up to 3 wk. Nutritional contents, consumer sensory acceptability, microbial population, color, and firmness of the apples were evaluated during cold storage. In 100 g of fresh-cut apples, vitamin E content increased more than 100 times, and calcium and zinc contents increased about 20 times compared with unfortified apples. Consumer sensory study demonstrated that HFCS-treated apples were highly accepted by consumers in respect to overall liking, color, and texture quality. Bacterial growth was concurrently detected in all apples, but the total plate accounts were under 2.6 log colony-forming units (CFU)/ g apple at the end of 7 d of storage, significantly lower than the industrial standard. Instrumental analysis indicated that VI treatment in both HFCS and CC solutions significantly decreased color change and retained the firmness of fresh-cut apples during 3 wk of cold storage.