John B. Golding

Extraction and isolation of catechins from tea

Tea is a major source of catechins, which have become well known for their antioxidant potential. Numerous human, animal, and in vitro studies have linked tea catechins with prevention of certain types of cancers, reduction of the risks for obesity, diabetes, and cardiovascular disease, and improvement of the immune system. Tea catechins are widely used in various neutraceuticals, pharmaceuticals, and cosmetics for either enhancing product shelf-life or for enhancing human health. Thus, the demand for catechins has increased considerably. Catechins have been extracted and isolated from tea leaves by numerous methods through several steps including: treatment of the tea leaves, extraction of catechins from teas into solvents, isolation of catechins from other extracted components, and drying the preparations to obtain catechin extracts in a powder form. This paper outlines the physical and chemical properties of the tea catechins and reviews the extraction steps of the various extraction methods, as a basis to improve and further develop the extraction and isolation of the tea catechins.

Optimizing conditions for the extraction of catechins from green tea using hot water

Six different factors involved in the extraction of catechins from green tea using water were examined for their impact on the yield of catechins and on the efficiency of water use. The best temperature and time combination for catechin extraction was at 80°C for 30 min. The yield of catechins was also optimal with a tea particle size of 1 mm, a brewing solution pH <6 and a tea-to-water ratio at 50:1 (mL/g). In terms of efficient use of water in a single extraction, a water-to-tea ratio of 20:1 (mL/g) gave the best results; 2.5 times less water was used per gram of green tea. At the water-to-tea ratio of 20:1 mL/g, the highest yield of catechins per gram of green tea was achieved by extracting the same sample of green tea twice. However, for the most efficient use of water, the best extraction was found to be once at a water-to-tea ratio of 12:1 (mL/g) and once at a water-to-tea ratio of 8:1 (mL/g). Therefore, all six of the factors investigated had an impact on the yield of catechins extracted from green tea using water and two had an impact on the efficiency of water use.

Isolation of Green Tea Catechins and Their Utilization in the Food Industry

Tea is a rich source of catechins, which are well-known antioxidants. Tea consumption has been found to promote human health; however, only drinking tea may not provide a sufficient level of catechins to achieve health benefits. Thus, the utilization of catechins in foods is an alternative way to supplement catechin consumption. Furthermore, catechins can prevent lipid oxidation and improve color and flavour of foods; hence, addition of catechins can also prolong the shelflife of foods. Therefore, catechins have recently been isolated from green tea for utilization in food products to enhance their shelflife and health benefits. This article outlines several methods for the isolation of catechins from green tea, discusses the challenges involved, and reviews the utilisation of catechins in the food industry.

Water Sorption Isotherm of Pea Starch Edible Films and Prediction Models

The moisture sorption isotherm of pea starch films prepared with various glycerol contents as plasticizer was investigated at different storage relative humidities (11%–96% RH) and at 5 ± 1, 15 ± 1, 25 ± 1 and 40 ± 1 °C by using gravimetric method. The results showed that the equilibrium moisture content of all films increased substantially above aw = 0.6. Films plasticized with glycerol, under all temperatures and RH conditions (11%–96%), adsorbed more moisture resulting in higher equilibrium moisture contents. Reduction of the temperature enhanced the equilibrium moisture content and monolayer water of the films. The obtained experimental data were fitted to different models including two-parameter equations (Oswin, Henderson, Brunauer–Emmitt–Teller (BET), Flory–Huggins, and Iglesias–Chirife), three-parameter equations Guggenhiem–Anderson–deBoer (GAB), Ferro–Fontan, and Lewicki) and a four-parameter equation (Peleg). The three-parameter Lewicki model was found to be the best-fitted model for representing the experimental data within the studied temperatures and whole range of relative humidities (11%–98%). Addition of glycerol increased the net isosteric heat of moisture sorption of pea starch film. The results provide important information with estimating of stability and functional characteristics of the films in various environments.

Optimum conditions for the water extraction of L‐theanine from green tea

Theanine is a unique non-protein amino acid found in tea (Camellia sinensis). It contributes to the favourable umami taste of tea and is linked to various beneficial effects in humans. There is an increasing interest in theanine as an important component of tea, as an ingredient for novel functional foods and as a dietary supplement. Therefore, optimal conditions for extracting theanine from tea are required for the accurate quantification of theanine in tea and as an efficient first step for its purification. This study examined the effects of four different extraction conditions on the yield of theanine from green tea using water and applied response surface methodology to further optimise the extraction conditions. The results showed that temperature, extraction time, ratio of water-to-tea and tea particle sizes had significant impacts on the extraction yield of theanine. The optimal conditions for extracting theanine from green tea using water were found to be extraction at 80 °C for 30 min with a water-to-tea ratio of 20:1 mL/g and a tea particle size of 0.5-1 mm.

Use of the nitric oxide-donor compound, diethylenetriamine-nitric oxide (DETANO), as an inhibitor of browning in apple slices

Summary Freshly-cut slices of apple (Malus domestica Borkh. ‘Granny Smith’) were dipped in a solution of the nitric oxide-donor compound, 2,2’-(hydroxynitrosohydrazino)-bis-ethanamine (diethylenetriamine-nitric oxide; DETANO) and the development of surface browning was examined during subsequent storage at 0°C. It was found that dipping in DETANO solution inhibited the development of browning, provided the solution was buffered to be slightly acidic. The most effective treatment to inhibit browning, and therefore to extend post-harvest life, was dipping for 60 s in a solution of 10 mg l–1 DETANO dissolved in phosphate buffer at pH 6.5. The extension in post-harvest life achieved by DETANO, over untreated slices, was about 170% and the extension in post-harvest life compared to water-dipped slices was about 100%. Solutions of buffered DETANO were found to be stable, as a similar extension in post-harvest life was obtained for five separate batches of apple slices dipped sequentially, five-times for 60 s each, over a 20 min period in the same solution.

Characterization of rice starch-ι-carrageenan biodegradable edible film. Effect of stearic acid on the film properties.

The main aim of this study was to develop rice starch (RS), ι-carrageenan (ι-car) based film. Different formulations of RS (1-4%, w/w), ι-car (0.5-2%, w/w) was blended with stearic acid (SA; 0.3-0.9%, w/w) and glycerol (1%, w/w) as a plasticizer. The effect of film ingredients on the thickness, water vapour permeability (WVP), film solubility (FS), moisture content (MC), colour, film opacity (FO), tensile strength (TS), elongation-at-break (EAB) of film was examined. Interactions and miscibility of partaking components was studied by using Fourier transform infrared spectroscopy (FT-IR) and X-ray diffraction (XRD). Hydrocolloid suspension solution of mix polysaccharides imparted a significant impact (p<0.05) on the important attributes of resulting edible film. TS and EAB of film were improved significantly (p<0.05) when ι-car was increased in the film matrix. Formulation F1 comprising 2% ι-car, 2% RS, 0.3% SA, Gly 30% w/w and 0.2% surfactant (tween®20) provided film with good physical, mechanical and barrier properties. FT-IR and XRD results reveal that molecular interactions between RS-ι-car have a great impact on the film properties confining the compatibility and miscibility of mixed polysaccharide. Results of the study offers new biodegradable formulation for application on fruit and vegetables.

From Apple to Juice—The Fate of Polyphenolic Compounds

Apples are a rich source of polyphenolic compounds and significantly contribute to the antioxidants in our diet. Apple variety affects the levels of those compounds; concentration can also be reduced during processing, especially juice production. These compounds have been linked with numerous health benefits. Reviews on the apple polyphenolic compounds and their health benefits exist; however, a review on maximizing the retention of the polyphenolic compounds in apple juice has not been compiled. Therefore, the purpose of this paper is to review the literature regarding apple polyphenolic compounds and the effects of processing techniques on their concentration in apple juice.

Physical and mechanical properties of a new edible film made of pea starch and guar gum as affected by glycols, sugars and polyols

The influence of different plasticizers (glycols, sugars and polyols) on the moisture sorption, mechanical, physical, optical, and microstructure characteristics of pea starch-guar gum (PSGG) film was studied. All plasticizers formed homogeneous, transparent, and smooth films, while PEG-400 did not produce film with suitable characteristics. Fourier transform infrared (FTIR) spectroscopy results indicated some interaction between plasticizers and the polymers. Scanning electron microscopy (SEM) observations of the films presented surfaces without cracks, breaks, or openings which were indicator of the miscibility and compatibility of employed plasticizers with PSGG films. The results showed that the films containing plasticizers with higher functional groups had lower equilibrium moisture content at aw <0.4. In general, a reduction in tensile strength and Youngs modulus and an increase in elongation at break were detected when molecular weight of plasticizers and relative humidity increased in all film formulations. Films plasticized with monosaccharide showed similar mechanical properties to those with sorbitol, but lower solubility and water vapour permeability (WVP), higher transparency and moisture content than the sorbitol-plasticized films. The most noticeable plasticization effect was exerted by following order: glycerol > EG > PG > xylitol > fructose > sorbitol > mannitol > galactose > glucose > sucrose > maltitol.

Optimisation of the phenolic content and antioxidant activity of apple pomace aqueous extracts

Response surface methodology (RSM) was used to optimise the parameters for phenolic extraction from apple pomace using water, extraction time, extraction temperature and pomace to water ratio. The responses from these parameters were evaluated by measuring the total phenolic content and antioxidant activity of extracts. The optimum extraction parameters found in this study were 30 min extraction time, 85°C extraction temperature and 0.05 pomace to water ratio. A verification experiment of these extraction parameters was performed, along with three other corroborative sets of parameters. There was no significant difference between the predicted and actual values, confirming that the predictions using the models obtained through RSM were valid.