Quality Characteristics and FTIR Research of Amorphophallus konjac K. Koch Cultivated under Forest

Kunlun LI, Ting YANG, Xia WANG, Xueying DONG, Xingguo ZHANG*

1. School of Life Science and Engineering, Southwest Jiaotong University, Chengdu 610031, China; 2. Affiliated Hospital of Chengdu University of Traditional Chinese Medicine, Chengdu 610072, China; 3. Sichuan Jinlin Pharmaceutical Co., Ltd., Emei 614200, China

Abstract [Objectives] This study aimed to evaluate the quality characteristics of Amorphophallus konjac K. Koch and study the tubers of A. konjac K. Koch by infrared spectroscopy and second derivative method. [Methods] Referring to industrial standards of China for agriculture and related documents, the quality characteristics of A. konjac K. Koch were determined; and using potassium bromide tableting method and Fourier transform infrared spectroscopy, the infrared spectrum and second derivative spectrum of A. konjac K. Koch were studied. [Results] The drying rate, total ash content, acid-insoluble ash content, water extract content, ethanol extract content and crude polysaccharide content of A. konjac K. Koch were above 14.00%, 4.57%-11.78%, 0.04%-4.87%, 26.31%-36.98%, 2.20%-7.95% and 40.25%-61.18%, respectively. The infrared spectra of A. konjac K. Koch of different origins were relatively close, and the differences were mainly in peak intensity. The peaks at 1 642, 1 322, 1 241, 1 154, 1 022, 863, 770 and 576 cm-1 were the main specific peaks. The main component was konjac glucomannan. [Conclusions] FTIR technology is simple and quick, and is suitable for quality control and sample identification of A. konjac K. Koch. This provides a scientific basis for the quality control and comprehensive utilization of A. konjac K. Koch cultivated under forest.

Key words Understory rotation, Amorphophallus konjac K. Koch, Quality characteristic, Infrared spectroscopy

1 Introduction

Dried tubers ofAmorphophalluskonjacK. Koch (Araceae) were called Yaoyu in ancient times, cold in nature and spicy in taste. Tubers are the main medicinal and edible part ofA.konjacK. Koch. The whole plant ofA.konjacK. Koch is poisonous, and its tubers are the most toxic.A.konjacK. Koch needs to be detoxified before consumption. In China,A.konjacK. Koch has a more than 2 000 years of planting history, and it is also a traditional Chinese medicine used by the people for disease treatment. Modern research shows thatA.konjacK. Koch contains about 60%-70% konjac glucomannan. In addition, it contains protein, amino acids, flavonoids, alkaloids, ceramides,etc. Konjac glucomannan is the main active ingredient ofA.konjacK. Koch. It is often used to treat diseases related to glucose metabolism, lipid metabolism, and immune function abnormalities, with effects of moisturizing the bowel, lowering blood sugar, lowering blood fat, and anti-tumor. In addition to the medical field, konjac glucomannan products are also widely used in the fields of chemical engineering and biological materials. In China, the excellent germplasm ofA.konjacK. Koch exists in Wanyuan, Sichuan. In this study, tubers ofA.konjacK. Koch cultivated in wasteland after imitating wild cultivation of gastrodia, coptis and other herbal medicinal materials (selenium-rich area) were used as the main experimental material, and those ofA.konjacK. Koch produced in Beichuan and Mount Emei of Sichuan (non-selenium-rich area) were used as the control. Referring to industrial standards of China for agriculture,ChinesePharmacopoeia(2015 edition) and related literature, the quality characteristics and specific infrared spectrum ofA.konjacK. Koch were studied systematically, aiming to provide a reliable scientific basis for quality control and comprehensive development and utilization ofA.konjacK. Koch resources in understory rotation.

2 Materials and methods

2.1 Materials

2.1.1A.konjacK. Koch samples. The experimental samples (Table 1) were collected from Wanyuan, Mount Emei and Beichuan of Sichuan Province. They were identified as tuber ofA.konjacK. Koch by the professor Zhang Xingguo from the Institute of Chinese Materia Medica of Southwest Jiaotong University.

Table 1 Sources of Amorphophallus konjac K. Koch samples

2.1.2Main instruments and reagents. The main instruments and equipment used were Fourier Transform Infrared Spectrometer (Spectrum One, Perkin Elmer, USA) (detector: DTGS), of which the spectral scanning range was mid-infrared, the wave number was 4 000-400 cm-1, the resolution was 4 cm-1, and the number of times of spectral scanning was 16 times, spectrum v6.3.2 software, tableting mold (13 mm in diameter), tablet press (YP-2, Shanghai Mountain Scientific Instrument Co., Ltd.) and electric heating blast drying oven (DHG-9240A, Shanghai Jinghong Experimental Equipment Co., Ltd.).

The reagents and drugs used mainly included potassium bromide (KBr) crystals (spectroscopically pure, Chemical Research and Design Institute of Zigong City, Sichuan Province), ethanol (analytically pure) and hydrochloric acid (analytically pure).

2.2 Methods

2.2.1Sample treatment. The collectedA.konjacK. Koch tubers were placed in flowing water to clean the surface sediment, preventing the surface ofA.konjacK. Koch tubers from being injured by cleaning machinery. In water, theA.konjacK. Koch tubers were cut into slices about 3-4 mm thick, which were then air-dried in a cool and ventilated place and dried in a constant temperature blast drying oven at 40 ℃.

2.2.2Determination of total ash and acid-insoluble ash. Contents of total ash and acid-insoluble ash were determined according to GB 5009.4-2010 (Determination of ash in foods).

2.2.3Determination of water extract and ethanol extract. Content of extract was determined with hot leaching method referring toChinesePharmacopoeia(2015 edition). For water extract, distilled water was used as the solvent; and for alcohol extract, 95% ethanol was used as the solvent.

2.2.4Determination of crude polysaccharide content. Crude polysaccharide ofA.konjacK. Koch was extracted with dilute alkali extraction method referring toChinesePharmacopoeia(2015 edition) and related literature. The content of crude polysaccharide extracted (%) was determined.

2.2.5Research on specific infrared spectrum. TheA.konjacK. Koch samples were dried, crushed and passed through No.6 sieve, respectively for use.

A certain amount (1-2 mg) of the powder of each sample was ground with potassium bromide crystals in an agate mortar to a uniform state and tableted to measure the infrared spectrum. The corresponding information of the spectra was recorded. The second derivative spectra were calculated using Spectrum v6.3.2 software. The spectral characteristics and chemical composition of the samples were analyzed, and the similarities and differences between the samples were explored.

3 Results and analysis

3.1 Quality characteristicsThe statistical results of quality indices ofA.konjacK. Koch cultivated under forest from different origins are shown in Table 2.

Table 2 Quality characteristics of Amorphophallus konjac K. Koch in understory rotation (n=3, %)

The water, total ash, and alcohol extract contents of the understoryA.konjacK. Koch planted in different production areas showed approximately the same changing trends, while the water extract and alcohol extract showed obvious opposite rules.A.konjacK. Koch had high moisture content. It means that the material powder contained a certain amount of water or some compounds contained some crystal water that could be released by heating, which affected the content of water extract. The results of comparative analysis show that the total ash content was high. The acid-insoluble ash content ofA.konjacK. Koch produced in Beichuan production area was relatively high. It suggests thatA.konjacK. Koch had a strong ability to accumulate inorganic substances or the cleaning and processing process was not standardized, which led to contamination of soil and other impurities.

In the experiment on the quality characteristics of understoryA.konjacK. Koch in different producing areas, it was observed that compared with those from Beichuan and Mount Emei,A.konjacK. Koch from Wanyuan showed excellent quality characteristics. The ash, moisture, water extract and polysaccharide contents all showed high values.

The main ingredients inA.konjacK. Koch are polysaccharides, which are also a key indicator of constant quality. There are a lot of water-soluble polysaccharide components in polysaccharides. The content of alcohol extract ofA.konjacK. Koch is generally low, indicating that there are a small amount of alcohol-soluble components inA.konjacK. Koch. But compared to that from low-selenium zone,A.konjacK. Koch from Wanyuan had relatively high alcohol extract content. For evaluating the quality ofA.konjacK. Koch in Wanyuan area, theChinesePharmacopoeia(2015 edition) can be used as a reference, and the minimum content of alcohol extract inA.konjacK. Koch is limited.

3.2 FTIRThe infrared spectra and second derivative spectra of the tubers of understoryA.konjacK. Koch from different origins were obtained using potassium bromide tableting method and Fourier transform infrared spectroscopy (Fig.1).

A.konjacK. Koch in understory rotation showed peaks at 3 355, 2 980, 1 642, 1 322, 1 241, 1 154, 1 022, 770, 576 and 520 cm-1. Among them, peaks at 1 642, 1 322, 1 241, 1 154, 1 022, 863, 770 and 576 cm-1were the main specific peaks. After comparison, it was found that the three batches of samples MY-02, MY-03 and MY-04 also had peaks near 1 410 cm-1; MY-01, MY-02, MY-03, MY-04, MY-05 showed peak around 863 cm-1; while MY-06 had none of them, indicating that the corresponding functional group at 863 cm-1does not exist in the sample MY-06,i.e., it is a compound lacking the functional group, or due to other reasons, the structure of the compound changed. Experimental research[8]shows that the peaks at 1 154, 1 022, 863 and 770 cm-1are the key peaks, and they are the key to determining the differences between samples, and the core of determining the authenticity of the samples.

Through the establishment of the FTIR spectra ofA.konjacK. Koch in understory rotation, we can quickly and accurately identify the powder ofA.konjacK. Koch. It is the key to ensure the authenticity of various samples. In addition, the establishment of FTIR spectra also helps to establish a method for authenticating medicinal powders and provides a stronger guarantee for the establishment of modern quality standards.

Note: From the top down: MY-01, MY-02, MY-03, MY-04, MY-05 and MY-06; the lower part is corresponding IR spectra and second derivative spectra.Fig.1 Specific FTIR spectra and second derivative spectra of Amorphophallus konjac K. Koch samples

4 Conclusions

A.konjacK. Koch in understory rotation showed excellent quality characteristics. The main component was konjac glucomannan, and water-soluble polysaccharides were the dominant. This type of ingredient is one of the key indicators of constant quality ofA.konjacK. Koch. In this study, FTIR one-dimensional spectrum and second derivative spectrum were used to position the key wave numbers of the characteristic components ofA.konjacK. Koch. It is a green and fast detection method, and can be promoted to more food quality control.

This study provides an accurate and intuitive method for the quality evaluation and authenticity identification of understoryA.konjacK. Koch. At the same time, the quality evaluation system of traditional Chinese medicine is introduced into plant quality control, providing reference for in-depth research on quality control and resource development and utilization ofA.konjacK. Koch.A.konjacK. Koch in understory rotation has good quality and high yield. The economic, social and ecological benefits are significant. It is a high-quality and high-efficiency agricultural economic crop variety that is worthy of application and promotion in the wild planting system of herbal Chinese medicinal materials such as gastrodia and coptis.