Lembe Samukelo Magwaza

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.

A Review of Destructive and Non-destructive Methods for Determining Avocado Fruit Maturity

Optimum harvest maturity is one of the important factors determining the quality of avocado fruit. Currently, avocado harvest maturity is mostly determined using markers or indices such as mesocarp oil, dry matter, or moisture content, all quantified destructively using representative samples of a batch in a consignment. Although useful, destructive techniques are time-consuming and results reflect properties of specific produce evaluated. High variation in maturity stages affect postharvest quality and the rate of ripening within a consignment, causing logistical difficulties. Emerging analytical techniques have particular advantages in non-destructive detection of food quality and safety. In this paper, destructive and non-destructive analytical methods and instruments for determining maturity parameters of avocado fruit are discussed. This review also looks at the trends in applying emerging optical and imaging techniques to the analysis of avocado fruit maturity and quality, in particular, visible to near infrared spectroscopy, ultrasonic system, ultrasound imaging, hyperspectral imaging, magnetic resonance imaging, and fluorescence imaging. On the basis of the observed trends, the technical challenges and future prospects for commercial application of these non-destructive techniques for maturity determination of individual avocado fruit are presented.

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.

Robust Vis-NIRS models for rapid assessment of soil organic carbon and nitrogen in Feralsols Haplic soils from different tillage management practices

Abstract Application of spectroscopy for assessment of soil nutrition in the field may be affected by the depth at which the radiation spreads to, the analysed nutrient, the nutrient level or management practices such as tillage systems. In this study, the use of visible to near infrared spectroscopy (Vis-NIRS) was explored as a technique to predict soil organic carbon (SOC) and soil organic nitrogen (SON) in different tillage management practices, varying rates of nitrogen and different depth distribution. The tillage treatments were no-till (NT), rotational tillage (RT) and conventional tillage (CT) and nitrogen was applied at a rate of 0, 100 and 200 kg/ha as lime ammonium nitrate. The reflectance spectra of samples from 0 to 10, 10 to 20 and 20 to 30 cm depths were acquired from all tillage treatments using a laboratory bench-top monochromator NIR Systems Model XDS spectrometer. Partial least square regression (PLSR) models were developed using leave-one-out cross validation method. The models were then tested on independent test samples (54) randomly selected from the total 324 samples. Principal component analysis (PCA) was used to differentiate SOC in different tillage treatments and different rates of nitrogen. The best prediction model was observed for SOC with the coefficient of determination (R 2 ) = 0.993, root mean square error of prediction (RMSEP) = 0.157% and residual predictive deviation (RPD) = 2.55 compared with R 2  = 0.661, RMSEP = 0.019%, RPD = 2.11 for SON. PCA was able to cluster soil samples according to the rates of applied nitrogen but not the tillage systems and depths. This study demonstrated the application of Vis-NIRS for analysis of SOC and SON from soils with varying levels of the nutrients. The robustness of developed models was associated with analysing samples from different depths and combining them during calibrations. Therefore, models developed in this manner were recommended for technicians in the field since they would warrant the assessment of soil in different tillage systems and in the entire rooting zone of crops.

Long-term impact of no-till conservation agriculture on abundance and order diversity of soil macrofauna in continuous maize monocropping system

ABSTRACT Unsuitable soil management in agriculture is known to results in the deterioration of soil health and the decline of biodiversity. The experiment tested whether no-tillage with mulch (NT), could boost biological activity of soil macrofauna population in continuous maize monocropping system compared with rotational tillage with mulch (RT) and conventional tillage (CT). Soil macrofauna was sampled at the end of the 2014/2015 growing season using 25 × 25 × 25 cm steel monoliths. The mean density of individual orders was higher (p < 0.001) under NT (46%) and RT (38%) compared with CT (16%). However, the Shannon-Weaver index revealed that the diversity and evenness of orders were similar for all treatments. Macrofauna patterns revealed that NT and RT contained higher (p < 0.001) population of Isoptera and Diplopoda. Isoptera was 51% and 17% higher in NT than CT and RT, while in Diplopoda, NT was 39% and 2% higher than CT and RT, respectively. It was concluded that NT and RT systems favoured the development of macrofauna communities in the studied maize continuous monoculture cropping system but did not favour order diversity of macrofauna. This suggests the importance of crop rotation for the development of the more diverse macrofaunal population.

Physiological responses of irrigated wheat (Triticum aestivum L.) genotypes to water stress

ABSTRACT The recent drought in South Africa has reduced the production of both dryland and irrigated wheat. This study evaluated physiological traits of irrigated wheat genotypes in response to water stress (WS) imposed at different growth stages. A 8 × 2 × 3 [(genotypes) × (water treatmets; stresses and non-stressed) × (growth stages; tillering, flowering and grain filling)] factorial experiment based on a randomised complete block design with three replicates was conducetd. In general, the rate of photosynthesis was unaffected by WS except for genotypes LM43 at tillering and LM98 at grain filling. Stomatal conductance (SC) and transpiration rate (Tr) followed the same treand except for genotype LM35 which reduced its SC and Tr significantly at grain filling. Instantaneous waster use efficiency (IWUE) of genotype LM35 and LM57 was unaffected (p > 0.05) by WS at tillering but at flowering stage it was affected. However, at grain filling IWUE was affected (p < 0.05) in genotypes LM35, ML57, LM79 and LM 98. The relative water content was unaffected at tillering except for LM35 and LM47 genotypes whereas at flowering LM57, ML79, LM83 and LM98 were affected. These results indicate some degree of drought tolerance of these genotypes at different growth stages.

Characterisation of pigeon pea (Cajanus cajan) landraces grown in two climatic zones in KwaZulu-Natal province, South Africa

Pigeon pea is an important legume in arid and semi-arid areas of the Sub-Saharan Africa. Knowledge of adaptation characteristics of genotypes would significantly enhance its production in diverse environments of the region. Field experiments were conducted at two sites, namely Makhathini and Newlands Research Stations, both in KwaZulu-Natal province, South Africa, to assess the variation in agronomic characteristics among six local landraces obtained from smallholder farmers. The six landraces were categorised based on seed coat colour according to farmers’ perception. Significant differences were observed among landraces with respect to plant height and time to 50% flowering, indicating phenotypic variability. The Light Brown-seeded landrace planted at Newlands flowered earlier (106 d after planting). The Dark Brown-seeded landrace flowered within 150 d at Makhathini and reached physiological maturity in 185 d, earlier than other landraces. The results of principal component analysis suggested that yield of the Light Brown-seeded landrace was associated with two important agronomic parameters, namely harvest index (HI) and pod mass. The Light Brown-seeded and Cream with Brown-seeded landraces were associated with desirable yield traits including grain yield, HI and pod mass and can, therefore, be recommended as suitable parental lines in crop improvement programmes to improve pigeon pea grain yield.

Effect of ultraviolet irradiation on postharvest quality and composition of tomatoes: a review

Ultraviolet (UV) irradiation has recently emerged as a possible alternative to currently used postharvest phytosanitary treatments. Research has also highlighted other benefits associated with UV irradiation in postharvest technology. This review presents the effects of UV irradiation on postharvest and nutritional quality of tomatoes. The application of UV irradiation on tomatoes is discussed including its effect on biological (respiration rate, ethylene production and microbial growth), physico-chemical (firmness, colour, total soluble solids and titratable acidity) and nutritional (vitamins, carotenoids, phenolic and antioxidants) quality. UV-treated tomatoes have shown resistance to microbial growth and decay. Although UV irradiation reduces the loss of vitamin C during storage, the loss of vitamin E remains a concern. UV treatments lead to higher antioxidant capacity, flavonoids and phenolic content. UV irradiation significantly reduced carotenoids in certain cultivars. Based on the literature reviewed, the success of UV irradiation treatments is cultivar-dependent. While improved retention of phytochemicals has been reported in UV-C treated fruit, increased losses have been reported in certain cultivars. Research efforts on the development of cultivar-specific UV irradiation protocols are warranted. The effect of harvest maturity and seasonal differences in the efficacy of UV treatments is required to be investigated.