A large quantity of plant wastes (such as wood scrap, rice bran, used tea leaves, and the dregs from squeezed fruit) is generated by the woodworking and food industries and agriculture. The recycling of these wastes is limited to their use in feed, fertilizer, fuel, and cosmetics. In this study, by using lignin that is one of the main components in plants, a new recycling method for plant wastes was designed. Lignin is a phenolic high-molecular-mass biopolymer based on phenylpropanoid units that are unique to vascular land plants.

The antioxidant capacity of lignin from used green tea leaves was evaluated by measuring its effects on the autoxidation of linoleic acid. Autoxidation of linoleic acid was reduced by 50% in the presence of tea leaf lignin. This effect was weaker than that of α‐tocopherol and t‐butylhydroxyanisole. However, lignin enhanced the antioxidant effects of α‐tocopherol, epigallocatechin gallate or acetone extracts of used tea leaves, with the antioxidant activity of lignin + acetone extracts of used tea leaves being nearly equivalent to that of α‐tocopherol and t‐butylhydroxyanisole. PRACTICAL APPLICATIONS The agricultural industry generates large amounts of botanical food by‐products, including used tea leaves, most of which are discarded. To determine whether lignin extracted from used green tea leaves has a practical application, we measured its effect on the autoxidation of linoleic acid, a model for the oxidation of fats. We found that lignin contained in used green tea leaves has an antioxidant effect, suggesting that used tea leaves in industrial waste may have potential applications as antioxidants for food oils and fats.

Lignin, a natural polymer composed of phenylpropane units, is an agglutination element in the cell wall of vascular plants. These units are referred to as guaiacyl (a), syringyl (b), and p-hydroxyphenyl, (c) phenyl-propane units (Fig. 1). They are connected in three-dimensional space by C-C and C-O-C bonds. Softwood lignin consists of (a), hardwood lignin of (a) and (b), and herb lignin of (a), (b) and (c). Lignin is taken up as a "dietary fiber" when vegetables and fruits are consumed. It is thought that dietary fiber is useful for the prevention of some diseases (such as cancer) although most is excreted without being digested. To clarify the influence of dietary fiber on an organism, it is important to examine the relationship between the dietary fiber and enterobacteria. It has been reported that cellulose, hemicellulose, and pectin, components of dietary fiber other than lignin, are metabolized by enterobacteria (Van Soest, 1978). On the other hand, it has also been reported that ferulic acid, a model compound of lignin, is metabolized by Enterobacter and Escherichia (Grbić -Galić, 1986).

An open-type electron paramagnetic resonance (EPR) spectrometer to measure a sample located outside a resonator was fabricated. As the resonator, the field modulation coils, and the main magnet were integrated on the resonator side in the sensor head, the space fora sample was opened. Thus, a large sample could be placed at the end of the resonator without much limitation on the size. For ah apptication of this apparatus, various coal masses were placed on the resonator of the sensor head and EPR measurements were performed nondestructively. It was found that the EPR signal intensity of coals showed a good correlation with the carbon-to-hydrogen ratio, one of the parameters for classifying coal.

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