Effect of chlorambucil on potato subnormal germination and quality
To investigate the effects of isopropyl N-（3-chlorophenyl）carbamate（CIPC）treatment on sprouting and quality preservation of potato tubers during sub-ambient temperature storage at 12 ℃， the Favorita potato cultivar was chosen as the test material， and changes in germination and nutritional quality of potato tubers sprayed with 0.3 g/kg of CIPC and its dynamic residue were evaluated after storage at 12 ℃ for 150 d. Unsprayed tubers stored for the same period at four ℃ and 12 ℃ were assessed as controls. The results indicated that 12 ℃ + 0.3 g/kg CIPC treatment facilitated the speed of starch conversion to reducing sugar while maintaining soluble protein content in potato tubers better than the control group at four ℃. CIPC treatment at 12 ℃ also significantly inhibited tuber respiratory intensity， reduced sprouting and weight loss， and preserved tuber nutritional quality better than the unsprayed group stored at 12 ℃. CIPC residual contents in potato peels and tuber flesh were lower than the residue limit standard（30 mg/kg）after short-term storage for 30 d. In summary，0.3 g/kg CIPC treatment can be used as a high-efficiency sprout suppressant for long-term storage of potato tubers at the sub-ambient temperature of 12 ℃.
Key words:
potato；isopropyl N-（3-chlorophenyl）carbamate（CIPC）；subnormal temperature storage；sprout inhibition；nutritional quality；dynamic residue
The potato (Solanum tuberosum L.) is the fourth largest food crop after rice, wheat, and maize and plays a vital role in human dietary nutrition. Currently, China ranks first in the world regarding potato cultivation and production. At the beginning of 2015, the Ministry of Agriculture and Rural Development proposed implementing a potato staple food development strategy to further advance China’s potato industry into a critical historical phase. However, storage is a constraint to the industry’s development, with conventional storage methods struggling to meet the year-round supply of fresh potatoes and processing materials. The most commonly used environmental conditions for long-term potato storage worldwide are subnormal temperatures of 8 °C to 12 °C and relative humidity of 85% to 90% when tuber respiration rates are reduced, and low-temperature storage can avoid the low-temperature glycation phenomenon of starch degradation to reducing sugars. However, potatoes have a distinct natural dormancy period, usually 2-3 months, after which they begin to sprout. Potato sprouting causes potential problems such as tuber deterioration, nutrient loss, and lobotropin accumulation, resulting in an annual loss rate of more than 30%, making it an urgent issue in potato storage.
Chlorantraniliprole [isopropyl N-(3-chlorophenyl)carbamate (CIPC)] has been tested in large-scale production as the most effective and commonly used commercial method to inhibit potato tuber sprouting. Studies have shown that CIPC has the most significant effect on potato sprout inhibition at 8-12 °C, with no adverse impact on the physiological and nutritional quality of the tubers during storage. In addition, the tubers need to be healed before CIPC treatment. Considering the safety and environmental concerns associated with using CIPC, the US Food and Drug Administration (FDA) and the US Environmental Protection Agency (EPA) have set a minimum residue limit of 30 mg/kg. Currently, domestic and international research has focused on the application form, method, and sprout suppression of CIPC. The studies at home and abroad have focused on the application formulations, processes, and sprout suppression effects of CIPC. Still, they have not been able to determine the impact of CIPC on the nutritional quality of potatoes stored at 12 °C sub-ambient. The study of healthy quality changes in potatoes stored at 12 °C and room temperature, especially in different tuber parts. The residue levels and degradation dynamics in other tuber parts have rarely been reported. Therefore, the present study was conducted with the short; Therefore, in this study, the short-dormant variety Fioreta potato was used as test material and treated with CIPC at 12 °C. The study was conducted to analyze the germination and quality patterns of the short-dormant variety Fioreta potato, which was stored at 12 °C under sub-normal conditions after CIPC treatment. The germination and quality patterns were analyzed and compared with those of storage at four °C and 12 °C sub-ambient. The residual dynamics of CIPC in different parts of the tuber skin and flesh were determined. The aim is to achieve long-term storage of potatoes at sub-ambient temperatures in combination with low doses of sprout inhibitors. Potatoes at sub-ambient temperatures and to provide technical support for developing the potato storage and processing industry. The aim is to achieve long-term storage of potatoes at sub-ambient temperatures combined with low doses of sprout inhibitors, providing technical support for the development of the potato storage and processing industry.
1. Materials and methods
1.1 Test material and treatment
The potato tested was Feiwu Rita, with oval tubers, pale yellow skin, and yellow flesh. Select tubers with no mechanical injury, no germination and greening, and single fruit weight of 100 g to 150 g. First, they were placed at a temperature of 10 ℃ to 15 ℃, relative humidity of 85% to 95%, and protected from light for two weeks. Then they were divided into two groups. The following three groups were treated, each with 120 tubers (including three replicates), and the relevant indicators were measured regularly every 30 days.
1) 4 ℃ group: stored in a high-precision fresh-keeping experimental box with a temperature of (4.0±0.5) ℃ and relative humidity of 85%~95%.
2) 12 ℃ group: stored in a high-precision fresh-keeping experimental box with a temperature of (12.0±0.5) ℃ and relative humidity of 85%~95%.
3) 12 ℃+0.3 g/kg CIPC group: spray the CIPC powder with an effective mass concentration of 0.3 g/kg (calculated on the mass of the potato) evenly on the surface of the potato, and after five days of treatment in a sealed bag, transfer to the temperature ( 12.0±0.5) ℃, relative humidity 85%~95% high-precision fresh-keeping experimental box for storage. Among them, the 0.3 g/kg CIPC treatment concentration is preferably obtained based on the results of the previous experiments (0, 0.1, 0.3, 0.5 g/kg).
1.2 Reagents and instruments
2.5% CIPC powder: Shouguang Jinyu Chemical Co., Ltd.; hydrochloric acid, ethanol, 3,5-dinitro salicylic acid, Coomassie brilliant blue (all of which are of analytical grade): Tianjin Beibei Tianyi Chemical Reagent Factory; methanol, acetonitrile (all are chromatographically pure): Shanghai Yuanye Biotechnology Co., Ltd. High-precision fresh-keeping experimental box (GH-330): Tianjin Jiesheng Donghui Fresh-keeping Technology Co., Ltd.; Fruit and Vegetable Respiration Tester (GXH-3051H): Beijing Junfang Institute of Physics and Chemistry; UV-Vis Spectrophotometer (T6): Beijing General Analysis Instrument Co., Ltd.; high-speed refrigerated centrifuge (Centrifuge 5804R): Germany Eppendorf company; high-performance liquid chromatograph (LC-20A): Japan Shimadzu company.
1.3 Index determination method
1.3.1 Germination rate and weight loss rate
The germination rate was counted with the first bud length of the tuber reaching 2 mm as the germination standard, and the formula was as follows. Germination rate/% = number of germinated tubers/total number of treated tubers × 100
The weight loss rate was determined by the weighing method, and the formula was as follows.
Weight loss rate/% = {weight before storage (g) – weight after storage (g))}/weight before storage (g) × 100
1.3.2 Determination of respiratory intensity
The potato respiration intensity was measured by a GXH-3051H fruit and vegetable respirator [17], and the results were expressed in mg CO2 (/kg h).
1.3.3 Determination of nutrient content
The starch content of potato was determined by acid hydrolysis, explicitly referring to GB 5009.9-2016 “Determination of Starch in Food Safety National Standard”; the reducing sugar content was determined by 3,5-dinitrosalicylic acid method; Soluble protein content was determined by Coomassie brilliant blue G-250 method.
1.3.4 Determination of CIPC residues
The potato residues were measured by CIPC on the potato skin (skin samples of 1 mm to 2 mm) and potato flesh, respectively. For details, refer to the method of Cheng Jianxin [9] with a slight modification. Accurately weigh 5.0 g each of potato skin and flesh, grind to homogenate, add methanol for ultrasonic-assisted extraction for 60 min, take out and dilute to 100 mL with methanol, and filter through 0.45 μm microporous membrane for testing. Chromatographic conditions: Kromasil C18 column (5 μm, 3.9 mm×150 mm), mobile phase: methanol:acetonitrile:=80:10:10 (volume ratio), flow rate 0.7 mL/min, injection volume 20 μL, detection wavelength 254 nm.
1.4 Statistics
The measurement results of each index were obtained from the mean value of 3 replicates, and all data results were shown as mean ± standard deviation; Duncan’s multiple comparisons were used for significant difference analysis at the 0.05 level using SPSS 19.0 software.
2.Results and Analysis
2.1 Changes in the germination rate of potato tubers under different treatments
The germination after the dormant period of the potato is the biggest problem during its storage, which not only causes the quality deterioration of the tuber, such as water loss and shrinkage but also accumulates toxic substances, such as solanine, around the bud eye. The effect of the germination rate during storage is shown in Figure 1.
It can be seen from Figure 1 that the potatoes began to germinate when stored at 12 °C for 60 d. With the prolongation of storage time, the germination rate was positively correlated with the storage time. However, the germination of potato tubers stored at a low temperature of 4 °C was delayed to 120 d, and the germination rate was only 2.3%. The germination of potato tubers treated at 12 ℃+0.3 g/kg CIPC was postponed to 90 days, and the germination rate was 2.6%. When stored for 150 days, the germination rate of potatoes treated at 12 ℃ increased to 33.0%, compared with 87.9% and 62.7% in the four ℃ and 12 ℃+0.3 g/kg CIPC groups, respectively. The difference reached a significant level (P<0.05). . The results showed that low-temperature storage at four ℃ had the most significant effect on inhibiting the germination of potato tubers. The 12 ℃+0.3 g/kg CIPC group also significantly slowed down the increase of tuber germination rate.
2.2 Changes in weight loss rate of potato tubers under different treatments
The effects of different treatments on the weight loss rate of potato tubers during storage are shown in Figure 2.
It can be seen from Figure 2 that the weight loss rate of tubers in the four ℃ groups and the 12 ℃+0.3 g/kg CIPC group was significantly lower than that in the 12 ℃ groups (P < 0.05). After 150 days of storage, the weight loss rate of the 12 ℃ groups reached 2.7%, the 12 ℃+0.3 g/kg CIPC group was 1.8%, and the four ℃ groups was 1.2%, which were 33.3% and 55.6% lower than the 12 ℃ groups, respectively. Therefore, whether it is 4 °C or 12 °C + 0.3 g/kg
CIPC treatment had a significant effect on reducing the weight loss rate of tubers.
2.3 Changes in respiration intensity of potato tubers under different treatments
The quality change of potatoes after harvest is closely related to their respiration intensity during storage [20]. The effects of different treatments on the respiration intensity of potato tubers during storage are shown in Figure 3.
It can be seen from Figure 3 that the changing trend of the respiration intensity of potato tubers stored at four ℃ is relatively gentle and remains at a low level as a whole, indicating that low-temperature refrigeration effectively inhibits the respiration metabolism of tubers. However, the respiration intensity of potatoes stored at 12 ℃ did not change much during the dormancy period of 0-60 d. Still, with the end of the dormancy period, the tuber respiration gradually became vigorous, and the respiration intensity of the 12 ℃ groups reached the pre-storage level when stored for 150 d. 4.4 times; the 12 ℃+0.3 g/kg CIPC group effectively inhibited the respiration of tubers, which decreased by 38.2% at the end of storage compared with the 12 ℃ groups (P<0.05).
2.4 Changes in nutritional quality of potato tubers under different treatments
The effects of different treatments on the starch content, reduced sugar content, and soluble protein content of potato tubers during storage are shown in Figure 4.
It can be seen from Figure 4A that starch, as the energy storage material of potatoes, is continuously consumed during storage, and the content tends to decrease as a whole, especially after 60 d of storage, the conversion of starch is accelerated to maintain the energy required for self-consumption and tuber germination. The reduced sugar content in tubers can be converted from starch, and the changes in the content of the two are closely related to the ambient temperature. In this study, storage at four °C significantly accelerated the conversion and consumption of starch, while the reduced sugar content gradually increased (Fig. 4B). In the middle and late stages of storage, the starch and reducing sugar contents of tubers stored at four °C were significantly lower and higher than those at 12 °C, respectively (P < 0.05), which was consistent with the results of low-temperature saccharification and had a significant impact on processing quality. When stored for 150 days, the starch content of the 12 ℃+0.3 g/kg CIPC group was higher than that of the 12 ℃ groups. The reduced sugar content was lower than that of the 12 ℃ groups, indicating that the 12 ℃+0.3 g/kg CIPC treatment inhibited the hydrolysis of starch, thereby reducing the synthesis of reducing sugar. Still, the difference between the two was insignificant (P>0.05).
It can be seen from Figure 4C that the soluble protein content of potato tubers after different treatments showed a trend of first decreasing, then increasing, and then decreasing. The increase within 30 d to 60 d of storage may be due to the loss of fresh weight of tubers or the germination of tubers—the enhancement of pre-related enzyme activity, which activates protein synthesis. After 60 days of storage, the soluble protein content of each group decreased with the protein metabolism degradation caused by tuber germination. At the end of storage, the soluble protein content of tubers stored at four ℃ was the highest, and the difference was significant compared with that at 12 ℃ (P<0.05), while 12 ℃+0.3 g/kg CIPC treatment had no significant effect on the soluble protein content of tubers (P>0.05).
2.5 Changes in CIPC residues in potato tubers
In this experiment, CIPC was used as an auxiliary sprouting inhibitor during the storage process of potatoes at sub-normal temperature (12 ℃), and its residues in potato skin and potato meat continued to decrease with time. The dynamic changes of CIPC residues during the storage of potato tubers are shown in Fig. 5.
It can be seen from Fig. 5 that CIPC in potato skin and potato flesh degrades to below the international residue limit (30 mg/kg) after short-term storage for 30 d; The degradation rates were both 3.78 mg/kg and 2.31 mg/kg, and the degradation rates were both as high as 98%, which was far lower than the international residue limit standard.
3 Conclusion
Low-temperature storage has a significant effect in inhibiting germination. In this study, the respiration intensity of potato tubers was significantly reduced under the condition of 4 ℃, and the germination rate and weight loss rate of tubers were also kept at the lowest level. Still, the problem at the same time was that the conversion rate of starch into reducing sugar significantly rose. while at 12 °C + 0.3 g/kg CIPC
Under the premise of effectively avoiding low-temperature saccharification and maintaining the nutritional quality of tubers, the treatment significantly inhibited the respiration intensity of tubers, thereby reducing the germination rate and fresh weight loss and the loss caused by germination during potato storage. Through the detection and analysis of CIPC residues in potato skins and potato flesh, the CIPC residues after short-term storage for 30 days were lower than the FDA and EPA limit standards, and the degradation rates were as high as 98% after long-term storage for 150 days, and there was no residual safety risk. Therefore, 12 ℃+0.3 g/kg CIPC treatment can replace low-temperature refrigeration to a certain extent as long-term storage of potato tubers under sub-normal temperature conditions.