Avocado firmness monitoring with values obtained by means of laser doppler vibrometry

Avocado (Persea americana Mill.) ripeness is usually evaluated by destructive firmness assessment, yet quality is notorious for being heterogeneous within a consignment. This problem, which is especially true for imported avocado fruit, lends itself to searching for non-destructive methods for firmness evaluation. Firmness of objects can be analysed by impulse-response. This technique utilizes recording of a vibration signature and interpretation of the resonant frequency. In this study a laser Doppler vibrometer (LDV) was used for non-contact recording. The aim of this study was to show the feasibility of using a LDV to monitor avocado firmness. In order to create avocado batches of different homogeneity, three groups were treated with and without ethylene, inside or outside a box. After day 0 a third of the fruit were transferred into boxes (325 L) to be treated with ethylene for 24 h. A third was kept in boxes untreated and another third was kept on open trays. Avocado fruit cultivar ‘Hass’ were ripened at 18°C and measured on days 0, 2, 3, 4 and 6. Individual fruit were impacted once and two LDV measurements were taken simultaneously at the stem-end and seed-end. This was repeated twice around the fruit. Force-deformation measurements in compression mode were performed by means of uniaxial testing (Instron model 5542) on two opposite sides (day 0 n=8, then n=24 i.e., 8 per treatment/d). Significant differences were found between firmness of avocados over time and across treatments. Firmness decreased exponentially as expected (304.1 to 2.1 N) over six days. The LDV results showed significant differences between days, treatments and laser-location. The resonant frequency of the fruit decreased linearly until day 4 and then decreased more slowly (1671 to 476 Hz). On average, the frequency found at the seed-end of the fruit was higher than the resonant frequency at the stem-end. This is thought to be due to the seed itself, which could influence the vibration pattern. Resonant frequencies showed good correlation to the logarithm of firmness (r=0.87) and therefore were shown capable of monitoring avocado firmness

The timing of exogenous ethylene supplementation differentially affects stored sweetpotato roots

The effects of continuous supplemental ethylene (10 μL L−1) timing on the physiology and biochemistry of sweetpotato roots during storage at 25 °C were examined. Alongside continuous ethylene or air treatments, a subset of the roots were transferred at dormancy break, from those previously stored in ethylene into air and vice-versa. The study showed distinctive ethylene-induced effects on the metabolism of individual sugars, phenolic compounds and phytohormones (abscisic acid and zeatin riboside) across the spatial gradient of the root flesh and skin tissues. Although ethylene flushing doubled root respiration, sprout growth was significantly suppressed. Supplementation of roots with ethylene after dormancy break effectively inhibited sprout growth as much as continuous ethylene alone. On the other hand, truncating ethylene application after dormancy release promoted vigorous sprout growth. After prolonged storage, ethylene treatment was associated with increased weight loss and incidence of proximal rots. Supplemental ethylene also accelerated the catabolism of monosaccharides, and promoted accumulation of phenolic compounds in the proximal root sections

Design and construction of a flexible laboratory-scale mixing apparatus for continuous ethylene supplementation of fresh produce

The design and construction of a laboratory-scale apparatus for generating variable concentrations and flow rates of exogenous ethylene for fresh produce supplementation during storage trials is described. A stock of compressed ethylene in nitrogen (5000 μl l−1) was blended into a continuous flow stream of air and diluted to the desired concentrations. The ethylene and air flow rates were controlled with calibrated mass flow control valves. An empirical mathematical model was derived for real-time variation of both the mixed concentration and flow rate during continuous flow. Validation of the model was performed using fresh sweet potato as a case study where a steady continuous ethylene concentration of 10 μl l−1 was achieved for three months. The bespoke system offers easy-to-manage ethylene supplementation for research

Non-destructive discrimination of avocado fruit ripeness using laser Doppler vibrometry

Consumers increasingly desire ready-to-eat avocado fruit, yet if supplies fall short of customer expectations, complaints follow, incurring considerable cost and waste. In the avocado sector, wastage due to destructive testing and inaccurate assessment of firmness is significant. The aim of this study was to evaluate whether non-destructive laser Doppler vibrometry (LDV) was capable of assessing avocado ripeness. Data were sourced from two trials using preclimacteric imported 'Hass' avocado fruit originating from Chile and Spain, ripened at 12 and 18 °C, respectively. Standard force-deformation measurements, and either single or simultaneous dual vibration time signals were recorded during shelf-life, and assessed against respiration and non-structural carbohydrate content. Resonant frequencies measured from fruit by means of LDV decreased two- to four-fold during ripening and this corresponded with a concomitant decrease in firmness (253 N –2 N). The capability of the LDV system to non-destructively discriminate between ripeness stages was demonstrated

Assuring potato tuber quality during storage: A future perspective

Potatoes represent an important staple food crop across the planet. Yet, to maintain tuber quality and extend availability, there is a necessity to store tubers for long periods often using industrial-scale facilities. In this context, preserving potato quality is pivotal for the seed, fresh and processing sectors. The industry has always innovated and invested in improved post-harvest storage. However, the pace of technological change has and will continue to increase. For instance, more stringent legislation and changing consumer attitudes have driven renewed interest in creating alternative or complementary post-harvest treatments to traditional chemically reliant sprout suppression and disease control. Herein, the current knowledge on biochemical factors governing dormancy, the use of chlorpropham (CIPC) as well as existing and chemical alternatives, and the effects of pre- and post-harvest factors to assure potato tuber quality is reviewed. Additionally, the role of genomics as a future approach to potato quality improvement is discussed. Critically, and through a more industry targeted research, a better mechanistic understanding of how the pre-harvest environment influences tuber quality and the factors which govern dormancy transition should lead to a paradigm shift in how sustainable storage can be achieved

Temporal variation of volatile compounds from Sri Lankan mango (Mangifera indica L.) fruit during ripening

Background Volatile compounds are considered as an important quality factor, as their aroma influences consumer acceptability. The type and concentration of volatile compound varies with genotype, pre- and postharvest factors. However, there is a paucity of information on volatiles from mango cultivars endemic to Sri Lanka (Willard, Karutha Colomban and Malgova). Therefore, volatile compounds were extracted from ripe fresh peel and pulp and analysed using gas chromatography-flame ionization detector (GC-FID). Results Ocimene was the major volatile organic compound (VOC) of cv. Karutha Colomban whilst terpinolene was dominant for mango cv. Willard in addition to α-pinene, 3-carene and β-caryophyllene. Myrcene, ocimene, β-caryophyllene, α-pinene and α-humulene contributed to cv. Malgova. Conclusion The variation of VOC concentration in mango fruit was significantly influenced by the ripening temperature. In general, mango peel contained higher amounts of VOCs than pulp

Prediction of ‘Nules Clementine’ mandarin susceptibility to rind breakdown disorder using Vis/NIR spectroscopy

The use of diffuse reflectance visible and near infrared (Vis/NIR) spectroscopy was explored as a non-destructive technique to predict ‘Nules Clementine’ mandarin fruit susceptibility to rind breakdown (RBD) disorder by detecting rind physico-chemical properties of 80 intact fruit harvested from different canopy positions. Vis/NIR spectra were obtained using a LabSpec® spectrophotometer. Reference physico-chemical data of the fruit were obtained after 8 weeks of storage at 8 °C using conventional methods and included RBD, hue angle, colour index, mass loss, rind dry matter, as well as carbohydrates (sucrose, glucose, fructose, total carbohydrates), and total phenolic acid concentrations. Principal component analysis (PCA) was applied to analyse spectral data to identify clusters in the PCA score plots and outliers. Partial least squares (PLS) regression was applied to spectral data after PCA to develop prediction models for each quality attribute. The spectra were subjected to a test set validation by dividing the data into calibration (n = 48) and test validation (n = 32) sets. An extra set of 40 fruit harvested from a different part of the orchard was used for external validation. PLS-discriminant analysis (PLS-DA) models were developed to sort fruit based on canopy position and RBD susceptibility. Fruit position within the canopy had a significant influence on rind biochemical properties. Outside fruit had higher rind carbohydrates, phenolic acids and dry matter content and lower RBD index than inside fruit. The data distribution in the PCA and PLS-DA models displayed four clusters that could easily be identified. These clusters allowed distinction between fruit from different preharvest treatments. NIR calibration and validation results demonstrated that colour index, dry matter, total carbohydrates and mass loss were predicted with significant accuracy, with residual predictive deviation (RPD) for prediction of 3.83, 3.58, 3.15 and 2.61, respectively. The good correlation between spectral information and carbohydrate content demonstrated the potential of Vis/NIR as a non-destructive tool to predict fruit susceptibility to RBD

Non-destructive methods for mango ripening prediction: Visible and near-infrared spectroscopy (visNIRS) and laser Doppler vibrometry (LDV)

With up to 19% of mango fruit being lost during ripening, the need for non-destructive technologies to predict internal physiochemical traits is paramount. This study compared two non-destructive technologies, visible and near-infrared spectroscopy (visNIRS) and laser Doppler vibrometry (LDV), for predicting the ripeness of mango fruit in two cultivars, ‘Kent’ and ‘Keitt’. An internal quality index (IQI) in ‘Kent’ was predicted using visNIRS (RP2 = 0.729, RMSEP = 0.532) using partial least squares regression, which gave a single measure for ripeness incorporating firmness, sweetness, and pulp colour. This model was improved by using the sum of the individual sugar contents (glucose, sucrose, and fructose) over the conventional total soluble solids (TSS) measure. LDV provided poor predictions of firmness (R2 < 0.5) in both ‘Kent’ and ‘Keitt’ using least squares regression line. The resonant frequency, as measured by LDV, decreased linearly with time, while firmness quantified destructively (quasi-static) showed an exponential decrease, suggesting the vibrational and destructive firmness measure distinct characteristics, which would contribute to poor model performance. These results showed that LDV is not suitable for assessing mango ripening. While visNIRS models have been successful at predicting quality traits, our results suggested that using individual sugar content in place of TSS can improve the prediction of ripening. This understanding of the strengths and limitations of both visNIRS and LDV, and how they relate to destructive quality measurements, can be used to improve postharvest management practices whilst reducing commercial losses in the mango industry

Textural, biochemical and micro-structural changes in mesocarp tissue of imported avocado from Peru during ripening

Avocado (Persea americana Mill.) fruit is a valuable product and notorious for the difficulties encountered in determining quality. Typically the degree of ripeness of many climacteric fruits, such as avocado, is measured by assessing flesh firmness. The aim of the presented work was to elucidate the temporal and spatial changes in texture, biochemistry and micro-structure in different avocado tissues from the same fruit. Fruit were first treated with ethylene and then ripened at 12°C. Samples were taken four times over 10 days storage. Maximum load and viscoelasticity of horizontally-cut slices from fruit (n=24) imported from Peru were measured during ripening. These texture parameters were measured using an Instron 5542 universal testing machine fitted with a 500 N or 5 N load cell. Non-structural carbohydrates (NSCs; viz. sucrose, mannoheptulose, perseitol) and fatty acid methyl esters from the same samples were identified and quantified using standard HPLC coupled to evaporative light scattering detection and gas chromatography coupled to flame ionisation detection, respectively. Samples taken from adjacent mesocarp tissue slices were examined: each specimen included the sclerenchymatic exocarp, fleshy mesocarp and endocarp including the coat of the seed. An analysis of variance was performed to elucidate the change of parameters during fruit ripening. NSC content and textural properties changed during ripening and showed spatial heterogeneity within individual fruit. Micro-structural changes were evident during the latter stages of ripening and coincided with fruit softening and degradation in mannoheptulose. These findings might be used to enhance quality monitoring of imported avocado fruit

Spatio-temporal postharvest changes in texture and fatty acid profiles in avocado fruit from different origins

The degree of ripeness of many climacteric fruits, such as avocado, can be correlated with fleshfirmness and other rheological properties. However, there remains a paucity of information on not only thepostharvest changes in texture of avocado fruit from different origins, but also on the spatial variation in texturewithin individual fruit. In addition, the relationship between changes in texture and lipid profile of fruit tissueduring postharvest ripening is unknown.The aim of the present study was to assess and discriminate between avocado cv. Hass fruit from threedifferent origins (viz. Spain, Peru and Chile) on the basis of temporal and spatial changes in both texture andfatty acid profiles of fruit flesh. Texture of different horizontally-cut slices from individual fruit within aconsignment was measured during ripening using a previously unreported technique. Maximum load, elasticityand viscosity of fruit tissue was measured using an Instron 5542 universal testing machine fitted with either a500 N or 5 N load cell. The same fruit slice was immediately snap-frozen in liquid nitrogen and freeze-driedprior to subsequent extraction, identification and determination of fatty acid methyl esters (FAME) profiles usinggas chromatography coupled to flame ionization detection (GC-FID). The results were used to differentiate avocado fruit into definable groups using partial least squares discriminant analysis. Significant differences inmaximum load, elasticity, viscosity were found in avocado fruit flesh during ripening, and between origins andto a lesser extent between different locations within the fruit. Lipid profiles showed dissimilar compositionaccording to origin and changed slightly from apex to base. The textural changes and lipid profile in avocadofruit is therefore related to origin and the spatial variation within individual fruit