Postharvest Physiological Deterioration Research Articles

Drying kinetics and effect of drying conditions on selected physicochemical properties of foam from yellow-fleshed and white-fleshed cassava (Manihot esculenta) varieties

Fresh cassava is highly susceptible to rapid post-harvest physiological deterioration due to the high water activity. Therefore, foam mat drying was considered as an alternative drying technique for preservation. The drying kinetics of white-fleshed cassava foam (air volume fraction = 0.26, overrun = 36.0 %) and yellow-fleshed cassava foam (air volume fraction = 0.24, overrun = 32.2 %) were studied. The influence of temperature and foam thickness on moisture removal ratio (MR), drying rate, diffusivity and some important physicochemical properties of the cassava foams (CSF) during drying were researched and compared with those of non-foamed cassava pulp (NFP). The cassava foams were dried to foam powders at temperatures of 50 °C, 65 °C and 80 °C and foam thicknesses of 6 mm, 8 mm and 10 mm. The CSF exhibited two falling rates. The CSF powders had significantly lower total cyanogenic glucosides content compared to the NFP powder, and a high retention of total carotenoids. The dry foam powders had higher lightness/luminosity (L*) values than dry pulp powders. Micrographs revealed interactions between starch granules and the hydrocolloids but microstructure was not affected by increasing temperatures.

Enhancing the Shelf-Life of Fresh Cassava Roots: A Field Evaluation of Simple Storage Bags

Postharvest physiological deterioration (PPD) of fresh cassava roots limits their shelf-life to about 48 h. There is a demand for simple, cheap, and logistically feasible solutions for extending the shelf life of fresh cassava roots in industrial processes. In this study, three different types of bag materials were tested, namely woven polypropylene, tarpaulin, and jute as a potential storage solution for cassava roots with different levels of mechanical damage. Microclimate related to temperature, humidity, and carbon di-oxide (CO2) was monitored in order to understand the storage conditions for up to 12 days. The results showed that fresh cassava roots could be stored for 8 days, with minimal PPD and starch loss (2.4%). However, roots with significant mechanical damage in the form of cuts and breakages had a considerably shorter shelf life in the storage bag, compared to whole roots and roots with retained stalk (peduncle) where roots are connected to the main plant. Wetting of the roots and bag material were not significant factors in determining the shelf life and starch loss. Carbon dioxide concentration in the stores was significantly correlated with the starch loss in fresh cassava roots and is proposed as a possible method for continuously and remotely monitoring starch loss in large-scale commercial operations and reducing postharvest losses.

Postharvest physiological deterioration in cassava: potential problems, possible inhibition, and resistant level identification

Cassava roots can only be utilized quickly because the roots suffer physiological damage in only 1–3 days after harvest because of postharvest physiological deterioration (PPD). Once the cassava roots are physiologically damaged, they cannot either be consumed or marketed. Indonesia is the second-largest cassava producer in Southeast Asia that is most used for food and feeds. Unless there is a solution, the PPD problem may become the main obstacle in cassava production. Therefore, finding solutions to the PPD problem in cassava is necessary, may be approached either by treatment to inhibit PPD occurrences, identification of tolerance accessions among cassava germplasm, and development of PPD tolerance cassava through breeding programs. In our research, the identification method was done by applying various staining methods to detect color changes associated with PPD symptoms during the cassava storage period and then compared to the conventional observation of PPD symptoms. Subsequently, the effective staining approaches are used to evaluate various genotypes’ responses in the cassava germplasm collections. Finally, the breeding approaches to develop PPD tolerance cassava varieties are outlined. Hopefully, with these research results, the solution for PPD problems associated with cassava production in Indonesia will be available.

Comparative Transcriptomic Analysis of Storage Roots in Cassava During Postharvest Physiological Deterioration

Cassava is an important starchy and food crop; however, the commercial value of cassava is seriously constrained by postharvest physiological deterioration (PPD). In this study, the molecular mechanism underlying PPD was studied by comparative physiological and transcriptomic analyses. Physiological analyses indicated that the contents of H2O2 and malondialdehyde (MDA), and the activities of superoxide dismutase (SOD) and catalase (CAT) all increased along with PPD development. Further transcriptomic analysis investigated the distribution of the differential expression profiling and identified a total of 10,347 differentially expressed genes (DEGs) during PPD. Notably, most of the genes encoding antioxidant enzymes and protein kinases showed significant upregulation at transcriptional levels, indicating the activation of antioxidant system and kinase-mediated signaling pathway during the PPD process. In addition, the genes involved in the starch synthesis pathway were repressed, whereas the genes associated with the starch degradation pathway were induced, thus leading to a decrease in starch content during the PPD process. Together, this study yields new insight into the transcriptional regulation network during the PPD process and provides potential gene resources for the delay of PPD in cassava.

Electrochemical quantification of the levels of hydrogen peroxide in cassava using glassy carbon electrode modified with chitosan/silver nano-hybrid

This study correlates the production of hydrogen peroxide in cassava with its rapid postharvest physiological deterioration (PPD). Chitosan/silver nanohybrid was synthesized and immobilized on glassy carbon electrode for improved detection of hydrogen peroxide in electrochemical studies. The cathodic peak current for the reduction of hydrogen peroxide to water and oxygen occurred at -550 mV and β-carotene contents of the cassava cultivars were quantified using UV-Vis spectroscopy at a wavelength of 480 nm. No significant amount of hydrogen peroxide was found in the root tubers on the first, second, third and fourth day. However, the production of hydrogen peroxide from the different cultivars on the fifth and sixth day after harvest was found to correlate with their respective β-carotene contents. The cultivar with the highest β-carotene content (Yellow roots- IBA070593: 0.0044 mg/g) was found to have the lowest level of hydrogen peroxide on day 5 and day 6: 0.096 mmol/g FW and 0.037 mmol/g respectively; while that with the least β-carotene level (White roots- IBA980505: 0.0000 mg/g) demonstrated the highest level of hydrogen peroxide content on day 5 and day 6: 0.177 mmol/g FW and 0.096 mmol/g respectively; and highest percentage increase from the fifth to the sixth day of the PPD process. It is seen from this study that an increase in the level of hydrogen peroxide indicates PPD, and that antioxidants with hydrogen peroxide scavenging properties can help increase shelf-life of cassava cultivars

Cassava shrunken-2 homolog MeAPL3 determines storage root starch and dry matter content and modulates storage root postharvest physiological deterioration

Key messageAmong the five cassava isoforms (MeAPL1–MeAPL5), MeAPL3 is responsible for determining storage root starch content. Degree of storage root postharvest physiological deterioration (PPD) is directly correlated with starch content.AGPase is heterotetramer composed of two small and two large subunits each coded by small gene families in higher plants. Studies in cassava (Manihot esculenta) identified and characterized five isoforms of Manihot esculenta ADP-glucose pyrophosphorylase large subunit (MeAPL1–MeAPL5) and employed virus induced gene silencing (VIGS) to show that MeAPL3 is the key isoform responsible for starch and dry matter accumulation in cassava storage roots. Silencing of MeAPL3 in cassava through stable transgenic lines resulted in plants displaying significant reduction in storage root starch and dry matter content (DMC) and induced a distinct phenotype associated with increased petiole/stem angle, resulting in a droopy leaf phenotype. Plants with reduced starch and DMC also displayed significantly reduced or no postharvest physiological deterioration (PPD) compared to controls and lines with high DMC and starch content. This provides strong evidence for direct relationships between starch/dry matter content and its role in PPD and canopy architecture traits in cassava.

Identification and functional prediction of lncRNAs during cassava post‐harvest physiological deterioration

AbstractCassava (Manihot esculenta Crantz) is an important staple food crop in Latin America and Africa. However, after harvest, the tuberous roots undergo rapid post‐harvest physiological deterioration (PPD), a known perishable phenomenon that usually appears within 72 h post‐harvest. Post‐harvest physiological deterioration largely reduces the quality and economic value of cassava tuberous roots, restricting the use of cassava as a raw material in the food industry. To analyze the regulatory roles of long non‐coding RNAs (lncRNAs) during PPD, whole systematic screening of lncRNAs was performed. In this study, 288 differentially expressed lncRNAs were identified from 2,787 high‐confidence lncRNAs during PPD. cis‐Acting analysis revealed 10 interested lncRNA–mRNA pairs, in which the neighboring protein‐coding genes were mainly related to ethylene signaling, calcium sensors, and transcription factors. trans‐Regulatory coexpression network analysis reported that lncRNAs were potentially associated with genes involved in the oxidation‐reduction process. These results present a broad vision of cassava lncRNAs during PPD and provide the potential candidates for genetic engineering to alleviate deterioration of tuberous roots.

Post‐harvest physiological deterioration in several cassava genotypes over sequential harvests and effect of pruning prior to harvest

SummaryConsumers, traders and processors consider post‐harvest physiological deterioration (PPD) an important constraint. In Experiment 1, PPD was assessed three consecutive years in roots from five genotypes through seven storage days. PPD, scopoletin and dry matter content (DMC) was recorded during storage. Year, genotype, duration of storage and their interactions were significant. PPD was associated with duration of storage period, DMC and scopoletin contents. Ambient moisture and temperature during storage influenced PPD. In Experiment 2, roots from seven clones were harvested 10 months after planting from 30 consecutive biweekly plantings. PPD was assessed 0, 2 and 7 days after harvest. In 13 harvests, roots from plants pruned six days earlier were also evaluated. Results indicated large seasonal variation across genotypes. Pruning reduced PPD and DMC. Complex and contrasting relationships among the variables analysed were found. There is no uniform model explaining the relationship between PPD and the independent variables considered.

Genomic analyses of heat stress transcription factors (HSFs) in simulated drought stress response and storage root deterioration after harvest in cassava.

Heat shock factors (HSFs) play crucial roles in various plant stress responses. However, the current knowledge about HSFs in cassava, an important crop, is still insufficient. In this research, we identified 32 cassava HSF genes (MeHSFs) and clustered them into three groups (A, B, C) based on phylogenetic analysis and structural characteristics. Conserved motif analyses showed that MeHSFs display domains characteristic to HSF transcription factors. Gene structure analyses suggested that 29 MeHSFs contained only two exons. All identified 32 cassava MeHSFs were distributed on 13 chromosomes. Their expression profiles revealed that the different MeHSFs were expressed differentially in different tissues, most high expression genes belonged to group A. The similar MeHSFs were up-regulated after treatment with both PEG and abscisic acid (ABA), which implied that these MeHSFs may participate in resistance to simulated drought stress associated with the ABA signaling pathway. In addition, several MeHSFs were induced during postharvest physiological deterioration (PPD) in cassava. Our results provided basic but important knowledge for future gene function analysis of MeHSFs toward efforts in improving tolerance to abiotic stress and PPD in cassava.

Novel Role of Ethanol in Delaying Postharvest Physiological Deterioration and Keeping Quality in Cassava

Massive economic losses and the decrease in quality of cassava are caused by postharvest physiological deterioration (PPD). However, an effective solution remains limited. In this study, the role of ethanol in the PPD of cassava was investigated and highlighted. Exogenous ethanol delayed PPD and reduced the accumulation of reactive oxygen species, while increased the underlying activities of superoxide dismutase, catalase, peroxidase, and 2,2’-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid) (ABTS) radical scavenging. Moreover, exogenous ethanol increased the endogenous levels of ethylene and melatonin, all of which are negative regulators of PPD. Notably, this study found that exogenous ethanol reduced the degradation of starch, but enhanced ascorbic acid content and carotenoid content. In summary, these results revealed the novel role of ethanol in delaying PPD and improving the quality of cassava tubes without ethanol residue, suggesting an effective and promising way in cassava.

The Class III Peroxidase (POD) Gene Family in Cassava: Identification, Phylogeny, Duplication, and Expression.

The class III peroxidase (POD) enzymes participate in plant development, hormone signaling, and stress responses. However, little is known about the POD family in cassava. Here, we identified 91 cassava POD genes (MePODs) and classified them into six subgroups using phylogenetic analysis. Conserved motif analysis demonstrated that all MePOD proteins have typical peroxidase domains, and gene structure analysis showed that MePOD genes have between one and nine exons. Duplication pattern analysis suggests that tandem duplication has played a role in MePOD gene expansion. Comprehensive transcriptomic analysis revealed that MePOD genes in cassava are involved in the drought response and postharvest physiological deterioration. Several MePODs underwent transcriptional changes after various stresses and related signaling treatments were applied. In sum, we characterized the POD family in cassava and uncovered the transcriptional control of POD genes in response to various stresses and postharvest physiological deterioration conditions. These results can be used to identify potential target genes for improving the stress tolerance of cassava crops.

Gene action and heterosis in F1 clonal progenies of cassava for β-Carotene and farmers’ preferred traits

Gene action and heterosis provides information to assist breeder for selecting and generating improved plant recombinants. This study aimed at determining the gene action of selected cassava traits. The F1 clones exhibited considerable phenotypic variability between families and offsprings. The best F1 progenies had a higher amount of β-carotene (β-C) of 6.12 mg 100 g−1 against 1.32 mg 100 g−1 of the best parent. This superiority could be attributed to the over-dominance from the recombination of additive gene action and epistasis. The general combining ability (GCA) of parents and specific combining ability (SCA) of combinations were significant for different traits, and indicating the role of additive and non-additive gene action in controlling such traits. The significant GCA for β-C and postharvest physiological deterioration (PPD) indicates the role of additive gene action. The significant SCA for cassava mosaic disease (CMD) and cassava brown streak disease (CBSD) showed a predominance of non-additive gene action. The F1 progenies from the family Mavoka x Garukunsubire expressed the highest positive heterosis for CMD, dry matter and β-C. The high positive heterosis for β-C and DMC could be linked to transgressive segregation, because one of the parents was poor combiner.

Relevance of Class I α-Mannosidases to Cassava Postharvest Physiological Deterioration.

Class I α-mannosidases (MNSs) play important roles in protein N-glycosylation. However, no data are currently available about MNSs in cassava (Manihot esculenta), of which the functions are therefore not known, particularly in relevance to postharvest physiological deterioration (PPD). A total of seven genes were identified from the cassava genome in the present study. Two (MeMNS2 and MeMNS6) of the seven genes may be pseudogenes, as indicated by sequence alignment and exon–intron organizations. Five MNSs could be classified into three subfamilies. Tissue-specific expression analysis revealed that MNS genes have distinct expression patterns in different tissues between sugar cassava and cultivated cassava varieties, indicating their functional diversity. A PPD response and defense model was proposed based on the transcription data of MNSs and genes involved in reactive oxygen species, signal transduction, and cell wall remodeling. The findings help in the understanding of PPD responses in cassava.

Effectiveness of pruning and waxing in reducing postharvest physiological deterioration in Uganda local cassava varieties

Cassava ( Manihot esculenta Crantz) roots in the fresh form, are susceptible to postharvest physiological deterioration (PPD), thus reducing their economic value and farmer benefits. The objective of this study was to evaluate the effectiveness of pruning and waxing on fresh root storability among cassava varieties in Uganda. Sixteen cassava plants per variety (TME 14, NASE 14, Nyaraboke, Kirimumpale, and Bukalasa) were pruned seven days before harvest, leaving the rest as unpruned controls. After harvest, roots were divided into two portions and one portion was waxed using food grade wax. Pruning alone reduced PPD of stored roots by 23% at day 14 of storage; and by 19% at day 28 compared with the control. Pruning as a treatment resulted into increased sugar content, ranging 9-30%), and significant (P 0.05) under the pruning and waxing treatment, which had minor effects on stored root composition. The results indicate that pruning is appropriate for the short-term storage of fresh cassava roots for up to 14 days. Waxing, combined with pruning, is suitable for longer term storage up to 28 days under Uganda conditions. Key words: Carbohydrate, Manihot esculenta , starch, storage

Expression profiles of defense genes in cassava storage roots upon exposure to Phytopythium sp., causal agent of soft root rot disease

Cassava is one of the most important crops in Africa, Asia and Latin America, where millions of people depend on its starchy storage roots as their main source of energy. In Brazil, cassava is cultivated in all regions; however, soft root rot disease has hampered its production mainly in the Amazon region. The identification of Phytopythium sp., as the causal agent of soft root rot disease in cassava plants collected in Brazil, was recently reported. Here, our main aim was to evaluate changes in expression levels of genes possibly involved in compatible cassava- Phytopythium sp. interaction. Semi-quantitative RT-PCR assays were performed to evaluate the expression levels of genes coding for proteins with known functions in plant defense, such as enzymes involved in oxidative burst and the phenylpropanoid pathway, in detached cassava storage roots inoculated and non-inoculated with pathogen. Our results showed that cassava responded to pathogen infection through up-regulation of genes coding for superoxide dismutase, phenylalanine ammonia-lyase, chalcone synthase, cysteine proteinase inhibitor and RING zinc finger protein. Furthermore, the expression pattern of the allergenic-related glutamic acid-rich protein and translationally controlled tumor protein genes in detached roots used here validated the absence of post-harvest physiological deterioration, a known endogenous disorder affecting the storage roots of cassava at 24–72 h after harvest. This is the first study of interaction between cassava and Phytopythium sp. at the molecular level contributing to understanding how cassava responds to pathogen infection, as well as to future strategies of molecular breeding regarding the tolerance to soft root rot disease.

Melatonin is involved in the regulation of postharvest physiological deterioration and quality of cassava tuberous roots

Melatonin is involved in the regulation of postharvest physiological deterioration and quality of cassava tuberous roots

Correlation of scopoletin-induced fluorescence with visible PPD symptoms in greenhouse cassava

Post-harvest physiological deterioration (PPD) is spoilage of cassava storage roots characterized by browning of parenchyma tissue and vascular streaking. A striking feature of PPD is an accumulation of hydroxycoumarins, such as scopoletin, scopolin, esculetin and esculin, which are products of phenylpropanoid pathway. PPD, which renders the roots unpalatable and unmarketable, leads to significant yield loss in global cassava production. Extensive studies have been conducted to understand the biochemical activities and pathways involved in PPD in which the result requires an evaluation of PPD symptoms which is usually based on a visual scoring system. However, high variations are consistently observed between biological replicates making analysis difficult. Therefore, there is urgent need to find a reliable marker since the generation of reliable data that can be shared or compared between institutions is desirable. The use of scopoletin-induced fluorescence as a PPD marker was tested in greenhouse-grown cassava storage roots by comparing fluorescence measurements and the PPD scores generated from normal light photographs of the harvested roots. It was found that all freshly harvested root samples lacked fluorescent but after 24 h they considerably fluoresced to a high level. However, the occurrence of intense fluorescence was not accompanied by intense PPD symptoms as fluorescence level declined when visible PPD symptoms developed. Hence, the use of fluorescence or scopoletin as an alternative marker for PPD remain unconvincing, mainly because it did not parallel with PPD symptom accumulation observed.

Effects of Calcium and Magnesium Fertilization on Antioxidant Activities during Cassava Postharvest Physiological Deterioration

The current research addressed the effect of fertilizers containing Ca2+ and Mg2+ on cassava (Manihot esculenta Crantz) storage roots (CSRs) during postharvest physiological deterioration (PPD). Cassava PPD tolerant and susceptible genotypes were grown in pots and treated with fertilizers containing Ca2+ or Mg2+. Eight months after planting, CSRs were harvested and stored at room temperature for 30 d. Morphological changes, antioxidant activities, mineral content, and starch content were determined. The results indicated that application of Ca2+ and Mg2+ fertilizers delayed PPD for >10 d in the susceptible genotype (SC5), but Mg2+ fertilizer elevated PPD in the tolerant genotype (QZ1). The Ca2+ fertilizer significantly increased fresh weight. A significant decrease in starch content in CSRs of SC5 treated with Mg2+ fertilizer was observed. The Mg2+ fertilizer slightly enhanced Ca2+, Mg2+, and K+ contents in both genotypes. In addition, Ca2+ fertilization led to a significant increase in H2O2 content and subsequent elevation of activities of catalase and peroxidase in both genotypes, especially at harvest. Our findings suggest that soil fertilization with fertilizers containing Ca2+ and Mg2+ may play a distinct role in PPD delay in CSRs.

Crosstalk between calcium and melatonin affects postharvest physiological deterioration and quality loss in cassava

Rapid postharvest physiological deterioration largely reduces the quality and marketability of cassava. The molecular mechanism underlying cassava postharvest physiological deterioration and quality loss is largely unknown. The present study aimed to investigate the role of calcium and its relationship with melatonin in cassava postharvest physiological deterioration. Transcriptomic analyses indicate that most of the calcium ion (Ca2+) sensor genes are upregulated in cassava tuberous roots at different postharvest stages. Exogenous CaCl2 reduces postharvest physiological deterioration, increases the endogenous levels of Ca2+ and melatonin, reduces the degradation of ascorbic acid and starch, and induces the expression of genes related to melatonin biosynthesis after harvest. These effects are reversed by the exogenous application of a Ca2+ chelator (EGTA). Exogenous melatonin also increases endogenous melatonin levels and reduces ascorbic acid and starch degradation during postharvest physiological deterioration but do not affect endogenous Ca2+ content. Together, these findings demonstrate that calcium-induced activation of melatonin biosynthesis plays a role in reducing postharvest physiological deterioration and quality loss in cassava. Additionally, pretreatment with EGTA arrests the melatonin-induced reduction of postharvest physiological deterioration, suggesting the possible crosstalk between melatonin and calcium during postharvest physiological deterioration.

Enzymatic Activity Prediction Using Time-Domain Nuclear Magnetic Resonance (TD-NMR) and Multivariate Analysis: A Case Study Using Cassava Roots

Time-domain nuclear magnetic resonance (NMR) has been widely used in food science. In this work, we demonstrate that the NMR decay obtained with the Carr–Purcell–Meiboom–Gill (CPMG) sequence can be used to estimate the peroxidase activity (PA) in cassava roots. This enzyme has been involved in post-harvest physiological deterioration (PPD), which limits the storage of fresh cassava to a few days. Cassava is a staple food for almost one billion people in tropical areas in Americas, Africa and Asia. A multivariate method using CPMG data and reference values of PA from a standard biochemical assay was built with 216 measurements for non-refrigerated and refrigerated samples of cassava roots. The figures of merit of the global partial least squares model using both types of roots showed a 0.06 μmol min−1 limit of detection (LOD) and a 0.2 μmol min−1 limit of quantification (LOQ) for PA, with 0.4 [intensity (a.u.)/(μmol min−1)] sensitivity and a standard error of cross-validation (SECV) of 0.7 μmol min−1. All of the results demonstrated that TD-NMR has the potential to predict PA in cassava roots that is indicative of the PPD problem.