Digital replica to unveil the impact of growing conditions on orange postharvest quality.

The postharvest end-quality of citrus is significantly impacted by pre-harvest factors such as weather, which varies among growing regions. Despite the importance of these factors, the influence of regional weather variations, such as variations in temperature, humidity, wind, vapor pressure deficit (VPD), and solar radiation on postharvest citrus quality, is largely unknown. This study aims to quantify this impact through a physics-driven digital replica of the entire value chain of Valencia oranges, from orchards in South Africa to retail in Europe. Predicted fruit properties data at harvest and hygrothermal sensor data from orchard to retail for different production regions are coupled to a physics-based fruit model to simulate key postharvest fruit quality metrics. These metrics include mass loss, chilling injury, fruit quality index (FQI), remaining shelf life (RSL), total soluble solids (TSS), and titratable acidity (TA). Our digital fruit model reveals that regional weather variability significantly affects fruit quality evolution when comparing data from Nelspruit, Letsitele, and Sunday's River Valley (SRV). The impact of weather variations is most pronounced in the temperate oceanic climate of SRV compared to the hotter climates of Letsitele and Nelspruit. Our findings indicate that differences in weather conditions between these growing regions impact postharvest mass loss, FQI, RSL, TSS, and TA of Valencia oranges at retail. The impact is up to 10% variation in mass loss and RSL, 4% in TSS, and 1% in TA among oranges grown in different regions. We show that temperature and humidity variations in the postharvest local transport of oranges between different regions largely increase mass loss by up to twofold, FQI by up to ~ 12%, and RSL by up to ~ 15% at retail. Our research also shows that weather temperature is the most important metric during fruit growth affecting various aspects of postharvest orange quality. This study offers valuable insights into the impact of regional weather variations on the quality of oranges available to consumers. These findings could help the citrus industry enhance growing practices, postharvest logistics, retail marketing, and cold chain strategies, thereby improving product quality and consumer satisfaction.

Product visibility in the South African citrus cold chain: Examining the efficacy of temperature loggers.

Product visibility is a challenge for many fruit cold chains. Most challenges arise because of technological constraints, which lead to the inability to predict whether fruit temperatures are still within the stipulated requirements. To ensure that the intricately linked cold chain for citrus fruit is well coordinated and offers the visibility of fruit temperature, technologies such as temperature data loggers are used to record and communicate temperature measurements. Concerns arise because temperature-monitoring loggers are not automated and therefore do not offer real-time temperature visibility. They require manual handling, which makes continuous access to temperature data impossible. Receiving real-time temperature data of citrus fruit during the different stages of the cold chain would enable exporters proactively to address issues linked to temperature as the citrus fruit moves along the supply chain. The aim of this study was to assess the potential value of using cellular loggers in contrast to conventional loggers to allow the real-time monitoring of citrus fruit in transit. At present, exporters cannot monitor the temperature conditions of their consignments during the critical phase of cold sterilisation at sea because conventional loggers do not provide visibility of temperature data. To determine the efficacy of cellular loggers, the researchers collected temperature data at the different stages of the cold chain. In addition, interviews were conducted with industry experts in the South African citrus cold chain to determine their experience with different loggers. These interviews identified that conventional (wired) loggers offer a low-cost option, but not real-time product visibility. Cellular loggers offer more real-time data than conventional loggers, but as they depend on cell-phone towers, they offer restricted real-time visibility, especially during the sea leg of the consignment. For this reason, the study recommends that the use of cellular temperature loggers be adopted during land-based stages of the citrus cold chain but not during the sea leg, despite exporters' concern about the limitations of conventional loggers.

A comprehensive analysis of carotenoids metabolism in two red-fleshed mutants of Navel and Valencia sweet oranges (Citrus sinensis).

Kirkwood Navel and Ruby Valencia are two spontaneous bud mutations of the respective parental lines of sweet orange (Citrus sinensis) Palmer Navel and Olinda Valencia, showing an atypical red pigmentation of the pulp. These red-fleshed varieties are commercially available and highly attractive for consumers but their carotenoid metabolism and the basis of the mutation have not been investigated. The red colour of Kirkwood and Ruby pulp was observed from the very early stages of fruit development until full maturity and associated with an altered carotenoid profiling. The red-fleshed varieties accumulated from 6- up to 1000-times more total carotenoids compared to the standard oranges. Specifically, the pulp of Kirkwood and Ruby accumulated large amounts of phytoene and phytofluene, and moderate contents of lycopene. Moreover, the red-fleshed oranges contained other unusual carotenes as δ-carotene, and lower concentrations of downstream products such as ß,ß-xanthophylls, abscisic acid (ABA) and ABA-glucosyl ester. This peculiar profile was associated with chromoplasts with lycopene crystalloid structures and round vesicles likely containing colourless carotenes. The flavedo and leaves of Kirkwood and Ruby showed minor changes in carotenoids, mainly limited to higher levels of phytoene. The carotenoid composition in Kirkwood and Ruby fruits was not explained by differences in the transcriptional profile of 26 genes related to carotenoid metabolism, covering the main steps of biosynthesis, catabolism and other processes related to carotenoid accumulation. Moreover, sequence analysis of the lycopene cyclase genes revealed no alterations in those of the red-fleshed oranges compared to the genes of the standard varieties. A striking event observed in Kirkwood and Ruby trees was the reddish coloration of the inner side of the bark tissue, with larger amounts of phytoene, accumulation of lycopene and lower ABA content. These observation lead to the conclusion that the mutation is not only manifested in fruit, affecting other carotenogenic tissues of the mutant plants, but with different consequences in the carotenoid profile. Overall, the carotenoid composition in the red-fleshed mutants suggests a partial blockage of the lycopene ß-cyclization in the carotenoid pathway, rendering a high accumulation of carotenes upstream lycopene and a reduced flow to downstream xanthophylls and ABA.

Digital twins enable the quantification of the trade-offs in maintaining citrus quality and marketability in the refrigerated supply chain.

Supply chains of fresh fruit must maintain a very narrow window of hygrothermal conditions after harvest. Any excursions outside this range can markedly lower the consumer acceptability of the fruit. However, the loss in fruit quality and marketability largely remains invisible to stakeholders throughout the supply chain. Here we developed a physics-based digital twin of citrus fruit to pinpoint when, why and to what extent fruit quality and marketability are reduced. Sensor data on 47 commercial shipments are thereby translated into actionable metrics for supply chain stakeholders by mapping the variability using principal component analysis. We unveiled a large spread (between 3% and 60%) in the shipments for different metrics of quality and marketability. Half of the shipments currently lie outside the ideal trade-off range between maintaining quality, killing fruit fly larvae and avoiding chilling injury. The digital twin technology opens the possibility to obtain the real-time coupling with sensor data to monitor food quality and marketability.

An Improved Systems Approach as a Phytosanitary Measure for Thaumatotibia leucotreta (Lepidoptera: Tortricidae) in Export Citrus Fruit From South Africa.

A systems approach was previously developed for mitigating phytosanitary risk of Thaumatotibia leucotreta (Meyrick) in citrus fruit exported from South Africa, as an alternative to a standalone cold disinfestation treatment. The present study first tested the original systems approach by applying it on a semicommercial scale in 10 Nova mandarin orchards. Fruit were inspected at points in the production, packing, and simulated shipping process, to assess performance of the systems approach. Additional data were obtained from 17 Valencia orange orchards and six packinghouses. In the second part of this study, the systems approach was accordingly revised and improved, consisting of three measures: 1) preharvest controls and measurements and postpicking sampling, inspection, and packinghouse procedures; 2) postpacking sampling and inspection; and 3) shipping conditions. The model quantifying the effectiveness of the systems approach was improved by correcting errors in the original version, updating parameter values and adding a component that provides for comparison with the risk mitigation provided by a standalone disinfestation treatment. Consequently, the maximum potential proportion of fruit that may be infested with live T. leucotreta after application of the improved systems approach is no greater than the proportion of fruit that may be infested after application of a Probit 9 efficacy postharvest disinfestation treatment to fruit with a 2% pretreatment infestation. The probability of a mating pair surviving is also determined. The model enables a priori determination of the required threshold levels for any of the three measures, based on quantification of the other two measures.

Light Regulation of Carotenoid Biosynthesis in the Peel of Mandarin and Sweet Orange Fruits.

Carotenoids are the pigments responsible for the coloration of the peel and pulp of Citrus fruits. Light is one of the major environmental factors influencing coloration and carotenoid content and composition of fleshy fruits and therefore their commercial and nutritional quality. Agronomical observations indicate that citrus fruits exposed to sunlight develop a brighter peel coloration than shaded fruit inside the tree canopy. In the present study, the effect of light deprivation on carotenoid profile, and in the expression of genes of carotenoid metabolism and their precursors have been analyzed in fruits of Clemenules mandarin (Citrus clementine) and Navelina orange (Citrus sinensis). Fruit shading accelerated peel degreening, chlorophyll degradation, and reduced chloroplastic-type carotenoids. Time-course shading experiments revealed that the stage of fruit ripening appears to be determinant for the effect of darkness in carotenoid biosynthesis. Fruit shading produced a down-regulation of the expression of key carotenoids biosynthetic genes (PSY, PDS, ZDS1, LCY2a, LCY2b, and CHX). However, expression of MEP pathway genes (DXS, HDR1, and GGPPS1) and the carotenoid cleavage dioxygenase, CCD4b1, responsible of the formation of the apocarotenoid ß-citraurin, were not substantially affected by dark-grown conditions. The content of abscisic acid (ABA), an end product of the carotenoid pathway, was not affected by the light regime, suggesting that effect of shading on the precursor's pool is not sufficient to impair ABA synthesis. A moderate increase in total carotenoid and in the expression of biosynthetic genes was observed in mature dark-grown mandarin and orange fruits. Collectively, results suggest that light stimulates carotenoid biosynthesis in the peel of citrus fruits but a light-independent regulation may also operate.

Rapid methods for extracting and quantifying phenolic compounds in citrus rinds.

Conventional methods for extracting and quantifying phenolic compounds in citrus rinds are time consuming. Rapid methods for extracting and quantifying phenolic compounds were developed by comparing three extraction solvent combinations (80:20 v/v ethanol:H2O; 70:29.5:0.5 v/v/v methanol:H2O:HCl; and 50:50 v/v dimethyl sulfoxide (DMSO):methanol) for effectiveness. Freeze-dried, rind powder was extracted in an ultrasonic water bath at 35°C for 10, 20, and 30 min. Phenolic compound quantification was done with a high-performance liquid chromatography (HPLC) equipped with diode array detector. Extracting with methanol:H2O:HCl for 30 min resulted in the optimum yield of targeted phenolic acids. Seven phenolic acids and three flavanone glycosides (FGs) were quantified. The dominant phenolic compound was hesperidin, with concentrations ranging from 7500 to 32,000 µg/g DW. The highest yield of FGs was observed in samples extracted, using DMSO:methanol for 10 min. Compared to other extraction methods, methanol:H2O:HCl was efficient in optimum extraction of phenolic acids. The limit of detection and quantification for all analytes were small, ranging from 1.35 to 5.02 and 4.51 to 16.72 µg/g DW, respectively, demonstrating HPLC quantification method sensitivity. The extraction and quantification methods developed in this study are faster and more efficient. Where speed and effectiveness are required, these methods are recommended.

Fruit shading enhances peel color, carotenes accumulation and chromoplast differentiation in red grapefruit.

The distinctive color of red grapefruits is due to lycopene, an unusual carotene in citrus. It has been observed that red 'Star Ruby' (SR) grapefruits grown inside the tree canopy develop a more intense red coloration than those exposed to higher light intensities. To investigate the effect of light on SR peel pigmentation, fruit were bagged or exposed to normal photoperiodic conditions, and changes in carotenoids, expression of carotenoid biosynthetic genes and plastid ultrastructure in the peel were analyzed. Light avoidance accelerated chlorophyll breakdown and induced carotenoid accumulation, rendering fruits with an intense coloration. Remarkably, lycopene levels in the peel of shaded fruits were 49-fold higher than in light-exposed fruit while concentrations of downstream metabolites were notably reduced, suggesting a bottleneck at the lycopene cyclization in the biosynthetic pathway. Paradoxically, this increment in carotenoids in covered fruit was not mirrored by changes in mRNA levels of carotenogenic genes, which were mostly up-regulated by light. In addition, covered fruits experienced profound changes in chromoplast differentiation, and the relative expression of genes related to chromoplast development was enhanced. Ultrastructural analysis of plastids revealed an acceleration of chloroplasts to chromoplast transition in the peel of covered fruits concomitantly with development of lycopene crystals and plastoglobuli. In this sense, an accelerated differentiation of chromoplasts may provide biosynthetic capacity and a sink for carotenoids without involving major changes in transcript levels of carotenogenic genes. Light signals seem to regulate carotenoid accumulation at the molecular and structural level by influencing both biosynthetic capacity and sink strength.

The use of Vis/NIRS and chemometric analysis to predict fruit defects and postharvest behaviour of 'Nules Clementine' mandarin fruit.

The use of chemometrics to analyse Vis/NIRS signal collected from intact 'Nules Clementine' mandarin fruit at harvest, to predict the rind physico-chemical profile after eight weeks postharvest was explored. Vis/NIRS signals of 150 fruit were obtained immediately after harvest. Reference data on the rind were obtained after eight-week storage, including colour index (CI), rind dry matter (DM), and concentration of sugars. Partial least squares (PLS) regression was applied to develop models. Principal component analysis (PCA) followed by PLS-discriminant analysis (PLS-DA) were used to classify fruit according to canopy position. Optimal PLS model performances for DM, sucrose, glucose and fructose were obtained using multiple scatter correction pre-processing, showing respective residual predictive deviation (RPD) of 3.39, 1.75, 2.19 and 3.08. Clusters of sample distribution in the PCA and PLS-DA models based on canopy position were obtained. The results demonstrated the potential applications of Vis/NIRS to predict postharvest behaviour of mandarin fruit.