The effect of tuber pre-heating temperature and storage time on the mechanical properties of potatoes

Reconditioning and weather conditions affect black spot damage during storage of potato (Solanum tuberosum L.) tubers

BACKGROUND

In potatoes (Solanum tuberosum L.), mechanical damage can cause the formation of black spots in the tuber flesh as the result of oxidation of phenolic compounds. This damage can result in substantial economic losses and degradation of quality. External factors contributing to the formation and the prevention of black spot damage (BSD) are not fully understood. The aim of this study was to determine the effect of weather conditions, using a hydrothermal coefficient, and of two potato tuber reconditioning methods on the formation of BSD. Five potato varieties were divided into high, moderate and low BSD susceptibility groups. The research was carried out over two growing seasons that differed greatly in precipitation and temperature. The black spot index was determined immediately after harvest and after 3 and 7 months of storage. Two reconditioning methods, applied for 7 days at 8 °C and for 7 days at 15 °C, were used for each variety.

RESULTS

The incidence of BSD in susceptible varieties did not depend significantly on weather conditions, although statistically significant variation was observed. We found a correlation between the hydrothermal coefficient (dry conditions) and BSD in the Etiuda variety. There was no significant effect of storage time and temperature on BSD incidence in susceptible or moderately susceptible varieties. The reconditioning methods significantly reduced the formation of BSD in tubers after storage in all three groups. Regardless of the level of susceptibility of the variety, storage time and storage temperature, the most efficient treatment to limit BSD was reconditioning for 7 days at 15 °C.

CONCLUSION

Identification of the significant effects of weather, and strong reduction of BSD in tubers that had been reconditioned, allows examination of the underlying mechanisms. The described reconditioning method can lead to satisfactory reduction of BSD in potato tubers. Data from this research will be of interest to potato breeders, particularly if valuable alleles that affect this phenomeon can be isolated. © 2019 Society of Chemical Industry.

Natural losses in tuber weight during storage as a predictor of susceptibility to post-wounding blackspot in advanced potato breeding materials

BACKGROUND

In potatoes, mechanical damage and the formation of black spots in the tuber flesh cause substantial economic losses and degradation of quality. The aim of this study was to determine the susceptibility of new potato genotypes (178 elite breeding lines) to blackspot damage after 7 months' storage at 5 and 8 °C, and to examine whether this susceptibility correlated with natural losses.

RESULTS

The lowest index of blackspot damage after harvest was found in genotypes from the mid-late group of earliness and low-susceptibility group, and after storage in genotypes from the early group of earliness and low-susceptibility group. After storage at 5 °C tubers were characterized by a lower susceptibility to bruising compared with tubers stored at 8 °C. The storage temperature significantly affected the natural losses in advanced potato breeding materials after storage in the case of all earliness and susceptibility groups. The highest susceptibility to blackspot damage and natural losses occurred in potatoes stored at 8 °C (r = 0.85-0.91). Such a relationship was not observed in potatoes stored at 5 °C.

CONCLUSION

For potato tubers susceptible to the formation of after-wounding blackspot, the natural losses arising as a result of storage at 8 °C can be used as a subjective method to evaluate the susceptibility of potatoes to the formation of black spots in the flesh. However, this observation needs further studies and stronger proof of this theory. © 2017 Society of Chemical Industry.

Application of Peleg's equation to describe creep responses of potatoes under constant and variable storage conditions

The application of Peleg's equation to characterize creep behavior of potatoes during storage was investigated. Potatoes were stored at 25, 15, 5C, and variable (fluctuating) temperature for 16 or 26 weeks. The Peleg equation adequately described the creep response of potatoes during storage at all storage conditions (R²  = .97to .99). Peleg constant k₁ exhibited a significant (p < .05) decreasing trend with storage time (t_s ) for samples stored under the experimental conditions whereas the constant k₂ appeared to be unaffected much by t_s except for samples stored at 25C. Under constant temperature storage, k₁ was found to be a linear function of t_s (R²  = .87 to .97). Also, the rate of change of k₁ appeared to be temperature dependent described by a linear relationship between the degradation rate constant for k₁ (α) and storage temperature (T). For the variable storage condition, a bulk mean temperature (T_bm ) was calculated to account for a series combination of storage time and temperature which the potatoes were subjected to. It was possible to describe the changes in k₁ due to variable storage temperature in terms of T_bm and t_s using stepwise multiple regression (R²  = . 94).

PRACTICAL APPLICATIONS

Precise description of the changes in the rheological properties of raw potatoes during storage could help predict the associated effect on the texture of cooked potatoes. Easy and simple methods of describing creep responses during storage or processing will be potentially helpful to better understand the phenomenon. The model parameters from such model could be used to relate rheological properties of raw and cooked potatoes. Moreover, the model parameters could be used to establish relationship between instrumental and sensory attributes which will help in the prediction of sensory attributes from instrumental data.

Effect of steam cooking on the residual enzymatic activity of potatoes cv. Agria

BACKGROUND

The aim of this work was to study the influence of steam cooking on pectin methylesterase (PME) and endogenous α- and β-amylase activities in different tissues (cortex and pith) of raw and heat-treated potatoes cv. Agria. Three different cooking temperatures were chosen (55, 70 and 85 °C). For each cooking trial, time-temperature profiles were recorded and the degree of cooking was expressed in terms of cooking factor.

RESULTS

Steam cooking contributed to significantly activate PME at 55 °C and to reduce its activity at the final processing temperature (85 °C), with the highest amount in the cortex (0.3745 ± 0.0007 µmol galacturonic acid (GA) g(-1) fresh weight (FW) min(-1) ) compared with the pith (0.2617 ± 0.0012 µmol GA g(-1) FW min(-1) ). The presence of heat-labile and heat-stable isoforms of PME in the considered potato tissues was also assumed. Heat treatment by steam resulted in a significant decrease in endogenous α- and β-amylase activities in both tissues compared with the raw potato, though without complete deactivation. Starch-degrading enzymes were also found to be differently distributed in the raw tuber.

CONCLUSION

Steam cooking affected in different ways the assessed residual enzymatic activity in the considered tissues of potatoes cv. Agria. Further research is needed to confirm the results obtained.