Paul J.R. Cronje

NIR Spectroscopy Applications for Internal and External Quality Analysis of Citrus Fruit—A Review

The global citrus industry is continually confronted by new technological challenges to meet the ever-increasing consumer awareness and demand for quality-assured fruit. To face these challenges, recent trend in agribusiness is declining reliance on subjective assessment of quality and increasing adoption of objective, quantitative and non-destructive techniques of quality assessment. Non-destructive instrument-based methods are preferred to destructive techniques because they allow the measurement and analysis of individual fruit, reduce waste and permit repeated measures on the same item over time. A wide range of objective instruments for sensing and measuring the quality attributes of fresh produce have been reported. Among non-destructive quality assessment techniques, near-infrared (NIR) spectroscopy (NIRS) is arguably the most advanced with regard to instrumentation, applications, accessories and chemometric software packages. This paper reviews research progress on NIRS applications in internal and external quality measurement of citrus fruit, including the selection of NIR characteristics for spectra capture, analysis and interpretation. A brief overview on the fundamental theory, history, chemometrics of NIRS including spectral pre-processing methods, model calibration, validation and robustness is included. Finally, future prospects for NIRS-based imaging systems such as multispectral and hyperspectral imaging as well as optical coherence tomography as potential non-destructive techniques for citrus quality assessment are explored.

Virtual cold chain method to model the postharvest temperature history and quality evolution of fresh fruit – A case study for citrus fruit packed in a single carton

Abstract Fruit quality loss is dependent on the temperature control throughout the postharvest cold chain. Previous research mainly focused on optimizing the cooling performance of single unit operations. However, assessing fruit temperature history throughout the entire cold chain is crucial to determine the end quality. This study proposes a virtual cold chain (VCC) method to predict the temperature history and quality loss of packaged fresh fruit, down to each individual fruit, throughout the entire cold chain. The VCC method is based on computational fluid dynamics and kinetic quality modelling. Results show that the difference in quality loss among individual fruit in a carton could reach 11% for a specific cold chain. The maximum difference in the remaining quality at the end of the cold chain between different cold chain scenarios is 23%. The VCC method has a potential to track temperature history and to estimate quality loss of individual fruit in the cargo throughout a cold chain.

Rapid methods for extracting and quantifying phenolic compounds in citrus rinds

Abstract 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.