Effects of Polygonatum odoratum Polysaccharides on the Quality of White Chili Peppers in Jars

Xiuqiang WANG, Li ZHOU, Chenzhong JIN, Yihong HU, Jing QIU, Yunyun ZHOU, Yan WANG

Abstract［Objectives］ This study was conducted to investigate the effects of Polygonatum odoratum polysaccharides on the quality of white chili peppers in jars. ［Methods］ White chili peppers were pickled by adding different concentrations of P. odoratum polysaccharides with traditional pickling technology， and its nitrite content， pH and sensory quality were analyzed and detected. ［Results］ The results showed that， compared with the control group without adding P. odoratum polysaccharides， the nitrite content in white chili peppers in jars decreased after adding P. odoratum polysaccharides. When the addition amount of P. odoratum polysaccharides was 0.002%， the inhibition rate of nitrite reached the maximum. Under the same fermentation time， P. odoratum polysaccharides could significantly reduce the pH value of pickles. When the addition amount of P. odoratum polysaccharide was 0.002% and the pickling time was 3 months， the sensory quality of white chili peppers in jars was the best. At this point， white chili peppers in jars had rich aroma and tasted soft and sour， and the sour and salinity were suitable. As the fermentation time continued to increase， the chili aroma of white chili peppers in jars gradually decreased， and the sour taste became more pronounced. ［Conclusions］ This study can provide reference for the safety and quality control of white chili peppers in jars.

Key wordsPolygonatum odoratum polysaccharides; White chili peppers in jars; Pickling process; quality

DOI：10.19759/j.cnki.2164-4993.2023.04.009

China is very rich in vegetable resources， with a production of 721 million tons in 2019 and a per capita share of 515.9 kg， both ranking first in the world［1］. The output value of vegetables accounts for the highest proportion of the entire agricultural output value， while pepper （Capsicum annuum L.） is the vegetable with the largest planting area， largest consumption， and most processing methods in China. The processing method of pickled white peppers is the most common for chili peppers. First， green peppers are blanched at high temperature and then exposed to the scorching sun to obtain through dehydration and decoloration， white chili peppers， which are then added with salt for pickling， and white chili peppers in jars are finally obtained after adding them into jars. White chili peppers taste soft， sour and spicy， with excellent layering， and have become an important side dish and flavored food in southern China［2］.

Pickling is the most commonly used processing method in China to change the taste and flavor of vegetables and improve their nutritional value. Due to simple process， easy preservation， unique flavor， and ability to enhance appetite， pickled vegetables are deeply loved by consumers.  However， in the fermentation process， it is easy to cause the loss of nutritional value of pickled vegetables and a nitrite content exceeding the standard. Nitrite has certain toxicity. When the human body ingests too much nitrite， it enters the blood to convert low ferrohemoglobin into methemoglobin， losing the oxygen carrying function and causing tissue hypoxia. Secondly， nitrite is easy to generate strong carcinogen， nitrosamine， in human body. Therefore， strict control of nitrite content in pickles plays a very important role in ensuring food safety and human health.

Polygonatum odoratum is a traditional medicinal and edible plant in China， in which Hunan P. odoratum and Sichuan P. odoratum having larger cultivation areas. Its rhizomes are often used for health care， prevention and treatment of metabolic syndrome such as hyperlipidemia， hyperglycemia， obesity and cardiovascular disease. P. odoratum is rich in a variety of bioactive substances and a variety of mineral elements needed by the human body［3］. P. odoratum can achieve different functions through the diversity of its components， including regulating blood sugar concentration， improving myocardial ischemia and antioxidant activity， and enhancing the bodys immune system. Our research team also found in the early stage that P. odoratum polysaccharides may inhibit the formation of obesity in high-fat diet rats by regulating the gut microbiota［4-5］. Recently， we have found that P. odoratum polysaccharides have good antioxidant activity， and are capable of significantly enhancing the activity of serum SOD， CAT， and GSH-Px in high-fat diet rats and reducing the content of MDA in the blood. Recently， it has been reported that the nitrite content of pickled vegetables can be controlled by adding redox substances， such as Vc and tea extracts［6-7］. Therefore， on the basis of previous studies， we speculated that adding P. odoratum polysaccharides can reduce the nitrite content in pickled vegetables. In order to verify our hypothesis， white chili peppers were used as raw materials to study the effects of different amount of P. odoratum polysaccharides added in the pickling process on the change of nitrite content in the product， so as to provide some reference for reducing the nitrite content in pickled white chili pepper products.

Materials and Methods

Materials and instruments

Main experimental materials： White chili pepper （Lianyuan Fengleyuan Agricultural Development Co.， Ltd.）; edible salt （Lianyuan Fengleyuan Agricultural Development Co.， Ltd.）; P. odoratum polysaccharides （extracted by the research team at the earlier stage）.

Main instrument： L3S visible spectrophotometer （Shanghai Yidian Analysis Instrument Co.， Ltd.）; electronic balance （Lianyuan Fengleyuan Agricultural Development Co.， Ltd.）.

Experimental methods

Pickling of white chili peppers in jarsPrepared white chili peppers were added into 1 L vegetable jars， each of which was filled with the same weight of white chili peppers and salt （2%）. The mouth of each jar was sealed with water， and then， white chili peppers were fermented in an indoor incubator at a constant temperature of 25 ℃.

Pickling method of white chili peppers in jars added with P. odoratum polysaccharidesOn the basis of normal fermentation， a certain amount of P. odoratum polysaccharide powder was added to white chili pepper jars， so that the concentrations of P. odoratum polysaccharides in the jars were 0.001%， 0.002%， 0.004%， and 0.006%， respectively.

pH determinationReferring to the method of Piao et al.［8］， the pH of white chili peppers in jars was determined.

Determination of nitrite contentAt the fermentation time of 1， 2， 3， 4， 5， and 6 months respectively， samples were taken from white chili peppers in jars with and without adding P. odoratum polysaccharide. The content of nitrite was determined by the N-naphthylethylenediamine dihydrochloride method［9］， with some modifications.

Analysis of sensory quality of white chili peppers in jarsTen teachers from the food major of Hunan University of Humanities， Science and Technology were selected for certain training. Based on the method of Liu et al.［10-11］ with some modifications， the quality of white chili peppers in jars was evaluated from four aspects： taste， smell， color， and shape. The average score of each quality was obtained， and the specific scoring standards are shown in Table 1.

Data processingSPSS 21.0 software was used for statistical significance analysis， and the experimental results were expressed in the form of mean±standard deviation （x±s）. The comparison of the mean values between two groups of samples was conducted using independent-sample t test， with P<0.05 being significant and P<0.01 being extremely significant.

Results and Analysis

Changes in pH content during the fermentation of white peppers in jars

During the fermentation process of white chili peppers in jars， changes in the main dominant microbial community can lead to changes in the pH of white chili peppers in jars， which can be used for predicting whether it is mature and the changes in its quality. The changes in pH value of white chili peppers in jars without or with the addition of P. odoratum polysaccharides under different fermentation time are shown in Fig. 1. Compared with the 1st month of fermentation， in the 3rd month of fermentation， the pH of white chili peppers in jars without or with the addition of P. odoratum polysaccharides significantly decreased， and both were less than 4.5， indicating that the white chili peppers in jars were basically fermented and matured at this time. Compared with the 3rd month， the pH value of the white chili peppers in the 4th month further decreased， but the rate of decrease slowed down. Moreover， there was no significant difference in the pH value of most white chili peppers in jars at the 3rd， 4th， 5th， and 6th months. However， after adding P. odoratum polysaccharides， the pH value of white chili peppers in jars was the lowest after the 6th month of fermentation， indicating that P. odoratum polysaccharides might provide a good environment for the growth of dominant bacteria such as lactic acid bacteria， thereby lowering the pH value of white chili peppers in jars. In addition， compared with 0.01%， 0.04% and 0.06% of P. odoratum polysaccharides， the pH value of white chili peppers in jars added with 0.02% of P. odoratum polysaccharides was the lowest， indicating that the decrease in pH value of white chili peppers in jars was not significantly dose-dependent on P. odoratum polysaccharides.

Effects of P. odoratum polysaccharides on nitrite content of white chili peppers in jars

Fig. 2 shows the dynamic change of nitrite content in white chili peppers in jars with and without the addition of P. odoratum apolysaccharides in the pickling process. For fermented white chili peppers in jars without and with P. odoratum polysaccharides， the nitrite content in white chili peppers in jars was the highest after 1 month of fermentation. In specific， the nitrite content in white chili peppers in jars without adding P. odoratum polysaccharides was 18.12 mg/kg， while the nitrite contents in white chili peppers in jars with 0.01%， 0.02%， 0.04% and 0.06% of P. odoratum polysaccharides decreased to 15.12， 14.19， 15.3 and 15.00 mg/kg， respectively， and the nitrite content of white chili peppers in jars added with 0.02% of P. odoratum polysaccharides was the lowest， which might be due to the fact that excessive P. odoratum polysaccharides were conducive to the growth of nitrate-reducing bacteria， causing the increase of nitrite in white chili peppers in jars. With the increase of fermentation time， the nitrite content in white chili peppers in jars generally decreased and then stabilized （<4 mg/kg）， which might be due to the decrease of dissolved oxygen in jars with the increase of fermentation time， which inhibited the growth of aerobic nitrate-reducing bacteria. Secondly， when the pH in jars was less than or equal to 4.5， the activity of nitrate reductase was reduced， thus inhibiting the formation of nitrite［12］.

Effects of P. odoratum polysaccharides on quality of white chili peppers in jars

The sensory quality scores of white chili peppers in jars without or with the addition of P. odoratum polysaccharides during the pickling process are shown in Fig. 3. For white chili peppers in jars without the addition of P. odoratum polysaccharides， as the fermentation time increased， the chili aroma of white chili peppers in jars became more and more intense， and the unique sour and spicy taste of white chili peppers in jars became more obvious. The coordination between sour and salty taste increased， and the sensory score of white chili peppers in jars first increased， reaching a maximum of 78 points in the 3rd month of pickling and fermentation. At this time， white chili peppers in jars had a rich aroma， and a delicious taste with moderate coordinated sour and salinity. Meanwhile， the shape of white chili peppers in jars was intact， without any cortical separation or severe damage， and no obvious vegetable chips were found. As the fermentation time continued to increase， a layer of white film appeared on the surface of white chili peppers， and white chili peppers gradually became soft in tissue， and exhibited damaged morphology， stronger source taste， and reduced palatability， so the sensory score significantly decreased. Compared with the control group， after adding different concentrations of P. odoratum polysaccharides to white chili peppers in jars， the sensory quality of white chili peppers in jars with different concentrations of P. odoratum polysaccharides was significantly improved at the same fermentation time. Under different concentrations of white chili peppers in jars， the optimal fermentation time for white chili peppers in jars was about 3 months. When the addition amount of P. odoratum polysaccharide was 0.002%， the sensory score of white chili peppers in jars was the highest， at 89 points. Meanwhile， the white chili peppers in jars had a strong aroma and no odor， and showed a unique pepper aroma. The taste was delicious， and coordinated in sour and salinity. From the 4th month of fermentation to the end of fermentation， the color， aroma， and taste of white chili peppers in jars decreased to a certain extent， and the texture gradually became soft. However， throughout the entire fermentation process， the shape of white chili peppers in jars was intact. In summary， it indicated that the addition amount of P. odoratum polysaccharides was optimal at 0.002%， and there was no dose dependence on the quality of white chili peppers in jars.

Conclusion and Discussion

At the initial stage of pickling and fermentation of vegetables， due to the presence of a certain amount of mixed bacteria on their surfaces and pickling utensils， and the fact that lactic acid bacteria have not yet formed a dominant strain， lactic acid fermentation is slow， and pH is high， and the growth of mixed bacteria is relatively rapid， reducing nitrate to nitrite. Therefore， nitrite is inevitably formed in the process of pickling vegetables［13］. As an important indicator affecting food safety， reducing the content of nitrite is very important.

In recent years， there have been many reports on the scavenging effect of plant extracts on nitrite. For example， flavonoids in the leaves of Styphnolobium japonicum can remove the content of nitrite in pickled cowpea［14］， and garlic extract can also remove the content of nitrite in salted fish［15］. In this study， it was found that adding P. odoratum polysaccharides could significantly reduce the nitrite content in white chili peppers in jars， and when the amount of P. odoratum polysaccharide was 0.002%， the nitrite content in white chili peppers in jars was the lowest. It showed that 0.002% was the best way to reduce nitrite content， which is consistent with the reported results of Astragalus membranaceus polysaccharides in scavenging nitrite ions［16］. In addition， our study found that polysaccharides from P. odoratum also reduced the pH value of white chili peppers in jars to a certain extent. Moreover， at higher concentrations， the pH value of white chili peppers in jars decreased faster， indicating that higher concentrations of P. odoratum polysaccharides had a stronger effect in promoting fermentation and acid production by lactic acid bacteria. Therefore， without affecting the taste of white chili peppers in jars， the concentration of P. odoratum polysaccharides can be appropriately increased. The study on the sensory quality of white chili peppers in jars found that the overall sensory quality of white chili peppers in jars was the best when the amount of P. odoratum polysaccharides added was 0.002% and the fermentation time was 3 months. At this point， the white chili peppers in jars had the unique spicy and rich aroma of white chili peppers， no peculiar smell， harmonious sour and salinity， and a refreshing and suitable taste.

In summary， P. odoratum polysaccharides improved the quality and safety of pickles to a certain extent. When the addition amount of P. odoratum polysaccharide was 0.002%， the physicochemical and sensory indexes of white chili peppers in jars were better than those with other concentrations. Therefore， in actual production and life， a certain concentration of P. odoratum polysaccharides can be added to white chili peppers in jars to improve its sensory quality and inhibit the production of harmful substances such as nitrite.

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Editor： Yingzhi GUANGProofreader： Xinxiu ZHU