Characterization of dragon fruit (Hylocereus spp.) components with valorization potential

Dragon fruit (Hylocereus spp.), also known as pitaya or pitahaya, is increasingly gaining interest in many countries, including Thailand which is a country with a climate ideal for breeding different varieties of tropical and subtropical fruits in general, and dragon fruit more specifically. The benefits of dragon fruit for human health can be explained by its essential nutrients such as vitamins, minerals, complex carbohydrates, dietary fibres and antioxidants. Dragon fruit is also an essential source of betacyanin which serves as a red/purple pigment with antioxidative properties. In Thailand, most of the fresh dragon fruits are consumed domestically, while some are traded globally as fresh fruit and processed products as juice or puree. As it is, dragon fruit peel and seeds are often considered as waste or by-products from fruit processing and have been less successful at adding value to the fruit. Currently, there is limited literature on dragon fruit properties, its processed products and constituents as well as potential utilization. Therefore, the main objective of this doctoral research was to gain deeper insight in the characteristics of dragon fruit and its derived products and components, specifically of two species of dragon fruit, i.e. white-flesh dragon fruit (H. undatus) and red-flesh dragon fruit (H. polyrhizus). The characteristics of these two species of dragon fruit and their possible application are extensively discussed in the doctoral thesis/research. Chapter 1 provides a state-of-the-art of current and relevant research on dragon fruit with respect to botanical classification, cultivation, economic aspects and chemical composition (particularly nutrients, pigment and antioxidative components) as well as an overview of techniques to process fruits (processing), i.e. freeze-drying and thermal processing. The impact of these processes on quality attributes (e.g. physicochemical and rheological properties) of different fruits is critically reviewed. The review also aims at giving a summarized overview of the most important aspects of seed oil (e.g. chemical composition and lipid oxidation) and cell wall polysaccharides (e.g. structure of pectic and hemicellulosic substances). In Chapter 2, the properties/characteristics of the whole fruit, peel, pulp (seed-free flesh) and puree (flesh containing seeds) of the two species of dragon fruit were performed. Results demonstrated that the peel of both dragon fruit species as well as the pulp and puree of the red-flesh species contained large amounts of betacyanin. As it is, they have the potential to be utilized as a natural colouring agent. Dragon fruit pulp and puree also exhibited significant antioxidative activities. This was even more pronounced for the red-flesh species due to the presence of betacyanin. The pulp and puree showed shear-thinning behaviour due to the presence of mucilaginous components. Throughout this doctoral research, these characteristics of dragon fruit, for example, pigment, antioxidative activities and rheological properties, provide a deeper insight with regard to further valorization of the fruit components and optimization of the fruit processing. Chapter 3 describes the characterization of the freeze-dried pulp and peel of the two species of dragon fruit to be further utilized of dragon fruit’s pigment (betacyanin) as a food additive. It was found that freeze-drying could satisfactorily preserve colour and pigment concentration. The freeze-dried red-flesh pulp and the freeze-dried dragon fruit peel from both species contained high contents of betacyanin. The freeze-dried dragon fruit pulp was well-soluble in water, whereas this was not the case for the freeze-dried dragon fruit peel. Additionally, due to the pH-sensitivity of betacyanin, the influence of pH (1-11) on the colour shift of the freeze-dried dragon fruit peel and pulp was monitored. The colour of the freeze-dried peel was stable within a pH range of 3-7, whereas the freeze-dried red-flesh pulp had high colour stability over a pH range of 1-11 and is available in a convenient form making it suitable for the use as a food colourant. In order to gain insight into the effects of thermal treatment on the characteristics of the white-flesh and red-flesh dragon fruit purees, the antioxidative, rheological, physicochemical and microbiological properties of the purees were investigated at different process conditions (between 50 and 90 °C for 60 min). The results are presented and discussed in Chapter 4. It is interesting to see that the antioxidative properties of the heated dragon fruit puree increased during heating treatment probably because of the superior antioxidative attributes of the dragon fruit seeds present in the puree and the formation of Maillard reaction products. During thermal processing, the L* value (lightness) and b* value (yellowness) of the processed dragon fruit puree can be used to control the quality online. Total colour change (TCC), which is an indicator of different colour between the unheated and heated puree samples, of the red-flesh dragon fruit puree showed a strong negative correlation with betacyanin content. The kinetics of colour changes and betacyanin degradation in the heated dragon fruit puree followed a second-order models. The apparent viscosity of the heated dragon fruit puree increased with heating time and temperature. The rheological data fitted very well with the power-law model, showing shear-thinning behaviour. Thus, the heated dragon fruit puree, particularly the red-flesh puree, offer possibilities to be applied in foodstuffs due to their interesting attributes after thermal treatment. The dragon fruit seeds are considered to have a high antioxidative potential. As it is, oil was extracted from the white-flesh and red-flesh dragon fruit seeds with petroleum ether as cold extraction. The characterization of the seed oil is described in Chapter 5. Dragon fruit seeds contained significant amounts of oil, which accounted for about 32-34% of the dried seed weight. The predominant fatty acids of both dragon fruit seed oils were linoleic acid (C18:2, 45-55%), oleic acid (C18:1, 19-24%), palmitic acid (C16:0, 15-18%) and stearic acid (C18:0, 7-8%), respectively. Dragon fruit seed oil is interesting from a nutritional point of view as it contains a high amount of essential fatty acids, amounting to 56%. The triacylglycerol (TAG) composition in the seed oil was also analyzed. It was shown to contain mainly triunsaturated and diunsaturated TAGs. A significant amount of tocopherols in the dragon fruit seed oil was clearly observed in which α-tocopherol was the most abundant tocopherol in the oil (72% of total tocopherol content). In addition, a storage assessment of 3 months was performed, monitoring the oxidative and tocopherol stabilities in the dragon fruit seed oil. A low oxidation rate of both dragon fruit seed oils was obtained, while tocopherol content decreased on storage. However, the concentration of tocopherols in the dragon fruit seed oil after 12 weeks remained high content compared to the initial state. Thus, the dragon fruit seed oil could be considered as a good source of essential fatty acids and tocopherols, with a high oxidative stability. In Chapter 6, the activity of pectic enzymes, i.e. pectin methylesterase (PME) and polygalacturonase (PG), of the pulp and peel of white-flesh and red-flesh dragon fruits as well as inactivation of pectic enzymes by thermal treatments (30-90 °C for 10 min) were examined. The untreated white-flesh dragon fruit had a higher PME activity compared to the red-flesh dragon fruit, whereas PG activity was absent in all dragon fruit samples. Results also demonstrated that no significant effects of PME activity at temperature below 70 °C for 10 min in either the pulp or the peel of dragon fruit were observed, while a moderate heat treatment (80 and 90 °C for 10 min) could efficiently inactivate PME. In the last part of this doctoral study, the polysaccharides (pectic and hemicellulosic substances) from cell wall materials of the pulp and peel of white-flesh and red-flesh dragon fruits were isolated and structurally compared, as described in Chapter 7. Prior to cell wall polysaccharide isolation, blanching at 80 °C for 10 min allowed PME inactivation. Subsequently, cell wall material was extracted and sequentially fractionated using various solutions to obtain three different pectic fractions, a hemicellulosic fraction and a remaining residue fraction which could not be solubilized by the procedure used. These polysaccharide fractions were chemically characterized in terms of galacturonic acid (GalA) content, degree of methoxylation (DM), neutral sugar composition, molar mass distribution and affinity towards some specific anti-pectin antibodies. Results showed that the cell wall polysaccharides in the pulp and, to an even greater extent, in the peel of both white-flesh and red-flesh species contained significant amounts of pectic substances. The pectic substances in the dragon fruit peel as well as in the dragon fruit pulp were shown to be lowly methyl-esterified pectin (DM < 39%) and highly water-soluble pectin (38-47%). A higher contribution of pectic homogalacturonan (HG) region in the peel samples was observed compared to the pulp samples, whereas there were no large differences between the pectic substances of both dragon fruit species. Despite the low average DM value of the pulp and peel pectins, pectic substances in both pulp and peel samples showed an affinity for anti-HG antibodies with different specificities, indicating that a wide range of epitopes (including long blocks of unesterified GalA residues as well as a few consecutive esterified GalA residues) was present. In this doctoral research, the key findings of the experimental work are clearly shown and summarized in Chapter 8. Dragon fruit is an excellent source of bioactive compounds such as betacyanin and tocopherol which both have high antioxidative properties and health-promoting functions. Dragon fruit also provides many valuable products and components that could have high potential of being applied in food industry. For example, the freeze-dried dragon fruit pulp could be used as a red/purple colouring agent (betacyanin) as well as an instant juice powder. The heated dragon fruit puree with significant antioxidative activity could serve as a semi-processed product, the dragon fruit seed oil, on the other hand, was defined as a high-value oil. The extracted cell wall polysaccharide from dragon fruit peel demonstrated to be a low methyl-esterified pectin. Thus, the dissemination of the research findings may significantly increase the value of dragon fruit, resulting in an increased revenue for growers and producers

Influence of drying process on total phenolics, antioxidative activity and selected physical properties of edible bolete (Phlebopus colossus (R. Heim) Singer) and changes during storage

<div><p>Abstract The research aimed to study the effect of hot-air drying on the properties of edible bolete mushroom (Phlebopus colossus (R. Heim) Singer). Fresh edible bolete contained an efficient antioxidant activity, showing a significant value of total phenolic content and radical scavenging activity and was high in protein and fiber with low fat content. The changes in physicochemical and antioxidative properties of edible bolete during hot-air drying at various temperature and time were studied. The phenolic content and antioxidative properties of edible bolete decreased with the temperature and drying time. At 60 °C for 5 h, the phenolic content and antioxidative properties of the dried edible bolete remained at 25% compared to the fresh mushroom. Moreover, there was no substantive change in the bacterial count of dried edible bolete with vacuum packing after six months at room temperature.</p></div

Rheological behaviour of dragon fruit purees as affected by thermal treatment

Two types of dragon fruit purees, white-flesh and red-flesh dragon fruits, were subjected to heat treatments for 0 to 60 min at temperatures between 50 and 90 °C, with the interval temperature of 10 °C. The influence of the different thermal treatments on the rheological behaviour was investigated during heating. The unheated white-flesh and red-flesh purees showed shear thinning behaviour, the viscosity decreased with increasing of shear rate range. After heating, the apparent viscosity of the purees increased with a function of thermal treatment and all cases of the purees fitted very well with power law model (R2 > 0.9988). The flow behaviour parameter of the heated purees varied between 0.89 and 0.99 for the white-flesh puree and between 0.69 and 0.85 for the red-flesh puree during thermal treatment while the consistency coefficient of the red-flesh puree showed significantly higher than that of the white-flesh puree. The effect of heating on the flow behaviour of the purees was more pronounced at high temperature region particularly the red-flesh puree, suggesting the red-flesh dragon fruit puree can probably be used for gel-system production which undergo high temperature and long time processing

Physicochemical properties, glass transition state diagram and colour stability of pulp and peel of two dragon fruit varieties (Hylocereus spp.) as affected by freeze-drying

The aim of the current study was to investigate the freeze-dried characteristics: physicochemical properties, colour parameters, total colour change, total betacyanins content and glass transition state diagram, of pulp and peel of white-flesh (Hylocereus undatus) and red-flesh (Hylocereus polyrhizus) dragon fruits. The results show that all dragon fruits can be successfully freeze-dried. For nutritional point of view, the retention of vitamin C counts up to 71.13% after freeze-drying. The water solubility of freeze-dried pulp was significantly different compared to the peel (p<0.05), that was about 7 times higher than that of the peel. Freeze-dried pulp and peel of red-flesh dragon fruit were a potential source of betacyanins content that found up to 360.14 mg/100 g. All freeze-dried dragon fruits obtained low glass transition temperature, varied between -6.70 and 4.83 °C. The visual colour of freeze-dried dragon fruits after rehydration was similar to their original colour. Thus freeze-drying seems to preserve the nutritional and colour properties of dragon fruits after processing. Furthermore, the impact of pH on the colour was also monitored due to the pH sensitivity of the red pigment, betacyanins present in the dragon fruit. The total colour change of all reconstituted freeze-dried gave very small value between pH 3 and pH 7 particularly the peel while the colour seriously changed at out of this pH range. Regarding to the finding results, it can be considered that the freeze-dried pulp of red-flesh dragon fruit can probably be used as a natural colorant due to relatively high in betacyanins, water solubility, vitamin C, and colour stability at low acid condition

Freeze-drying qualities and state diagram of pulp and peel freeze-dried dragon fruits (Hylocereus spp.)

Freeze-drying has been proposed to preserve nutritional values and colour of foodstuff. Moreover, few studies disrobe the influence of freeze-drying on the quality characteristic of tropical fruit, like dragon fruit. In this work, freeze-drying characteristics, vitamin C, betacyanins content, L*, a* and b* colour parameters and state diagram of pulp and peel of white-flesh (Hylocereus undatus) and red-flesh (Hylocereus polyrhizus) dragon fruits were investigated after freeze-drying. The effect of pH level on the colour was monitored due to the pH sensitivity of the red pigment, betacyanins present in dragon fruit. The results show that dragon fruit can be successfully freeze-dried. For nutritional point of view, the retention of vitamin C was high and count up to 71.13% after freeze-drying. Freeze-dried pulp and peel of red-flesh dragon fruit were a potential source of betacyanins particularly the peel. The water solubility of freeze-dried pulp of both dragon fruit types was up to 7 times higher than that of the peel. The visual colour of reconstituted sample unchanged at their natural pH and shows only a small changes between pH 3 and pH 7. All cases of freeze-dried dragon fruits obtained low glass transition temperature that varied between -6.70 and 4.83 °C. However, it can be considered that the freeze-dried dragon fruits can probably be applied for food processing

Comparative study of cell wall polysaccharides from pulp and peel of dragon fruits (Hylocereus spp.)

Cell wall polysaccharides from the pulp and the peel of white-flesh and red-flesh dragon fruits (Hylocereus spp.) were isolated using various solvents in order to obtain different pectin fractions. The galacturonic acid (GalA) content, the degree of methoxylation (DM), the neutral sugar composition and the molar mass distribution of these pectin fractions were determined, as well as their affinity towards some specific anti-pectin antibodies. The results showed that cell wall polysaccharides of dragon fruit samples contained significant amounts of pectic substances with a low average DM value. No remarkable differences between the pectic substances of the different dragon fruit varieties were observed while there were large differences between the pectic fractions of the peel and the pulp samples. The pectic substances in the peel are fairly linear and highly water-soluble whereas in the pulp, on the contrary, pectin is more branched and contains comparable amounts of loosely-bound, ionically-bound and strongly-bound pectic fractions. Using anti-pectin antibodies with different specificities (towards different pectin structures), it was revealed that a wide range of epitopes, including long blocks of unesterified GalA residues as well as blocks with consecutive esterified GalA residues, are present in the pectin fractions of peel/pulp dragon fruits

Characterisation of the physicochemical properties of two species of dragon fruit seed oil (Hylocereus undatus and Hylocereus polyrhizus)

Oil was extracted from the seed of white-flesh (Hylocereus undatus; WFSO) and red-flesh (Hylocereus polyrhizus; RFSO) dragon fruits using a cold extraction process with petroleum ether. The delta-, gamma-, and alpha-tocopherol content, fatty acid and triacylglycerols composition, thermal and rheological properties of the extracted dragon fruit seed oils were analysed. The results showed that the dragon fruit seeds contained a high amount of oil up to 34.13%. The principal tocopherol in WFSO and RFSO was alpha-tocopherol. The total tocopherols content of RFSO was 1.6 times higher than that of WFSO. The three main fatty acids in these oils were palmitic acid (C16:0), oleic acid (C18:1) and linoleic acid (C18:2). The seed oil is interesting from a nutritional point of view: the essential fatty acid content of WFSO and RFSO counts up to 55.64% and 45.37% respectively. The thermal curves for WFSO and RFSO consisted of five endothermic peaks and two crystallisation curves with a broader temperature range. The apparent viscosity of WFSO and RFSO was similar (14.24-14.32 mPa.s). Thus the dragon fruit seed oils can be considered as a new source of tocopherols and essential fatty acids

Characterisation of the physicochemical properties of two species of dragon fruit seed oil (Hylocereus undatus and Hylocereus polyrhizus)

Oil was extracted from the seed of white-flesh (Hylocereus undatus; WFSO) and red-flesh (Hylocereus polyrhizus; RFSO) dragon fruits using a cold extraction process with petroleum ether. The delta-, gamma-, and alpha-tocopherol content, fatty acid and triacylglycerol composition, thermal and rheological properties of the extracted dragon fruit seed oils were analysed. The results showed that the dragon fruit seeds contained a high amount of oil up to 34.13%. The principal tocopherol in WFSO and RFSO was alpha-tocopherol. The total tocopherols content of RFSO was 1.6 times higher than that of WFSO. The three main fatty acids in these oils were palmitic acid (C16:0), oleic acid (C18:1) and linoleic acid (C18:2). The seed oil is interesting from a nutritional point of view: the essential fatty acid content of WFSO and RFSO counts up to 55.64% and 45.37% respectively. The main triacylglycerol in WFSO and RFSO was LLL, LLO, PLL, LOO and PLO. The thermal curves for WFSO and RFSO consisted of two main endothermic peaks with a broader temperature range around these peaks of -49.58 and 3.41 °C. The apparent viscosity of WFSO and RFSO was similar (14.24-14.32 mPa.s). Thus the dragon fruit seed oils can be considered as a new source of tocopherols and essential fatty acids

ผลของปริมาณแป้งกล้วยหอมเขียวทดแทนแป้งสาลีที่มีต่อคุณลักษณะของขนมปัง

วารสารวิชาการและวิจัย มทร.พระนคร, ปีที่ 15, ฉบับที่ 1 (ม.ค.-มิ.ย. 2564), หน้า 1-13The objective of this research was to study the effect of substitution of wheat flour with Cavendish banana flour on specific volume, density, antioxidant activity, and the sensory acceptance of bread using Cavendish banana flour instead of wheat flour as 0% (control), 10%, 20% and 30% of the total flour weight. It was found that an increasing amount of Cavendish banana flour caused the darker of the bread appearance, and the specific volume of the bread decreased from 4.22 to 2.69 cm3/g, while the bread density increased from 0.24 to 0.37 g/cm3. The total phenolic content and antioxidant activity of the bread made of Cavendish banana flour instead of wheat flour were significantly greater than the control bread (p0.05) . Therefore, the bread using 30% Cavendish banana flour gave the highest amount of total phenolic compounds and antioxidant activity with well accepted by consumers.Rajamangala University of Technology Phra Nakho

An explorative study on the cell wall polysaccharides in the pulp and peel of dragon fruits (Hylocereus spp.)

The pectic and hemicellulosic cell wall polysaccharides from the pulp and the peel of white-flesh and red-flesh dragon fruits (Hylocereus spp.) were isolated and compared in terms of degree of methoxylation (DM), solubility properties (relative content of uronic acids and neutral sugars in different fractions), neutral sugar composition, molar mass distribution, and affinity towards some specific anti-pectin antibodies. Hereto, the alcohol insoluble residues were extracted and sequentially fractionated using hot water, a chelating agent, sodium carbonate, and potassium hydroxide solutions to obtain different pectin fractions and a hemicellulose fraction. Chemical analyses were used to characterize these polysaccharide fractions. The results show that cell wall polysaccharides of the pulp and especially of the peel from white-flesh and red-flesh dragon fruits contain significant amounts of pectic substances that are lowly methyl-esterified. The cell wall polysaccharides of the peel as well as those of the pulp contain high amounts (38-47%) of loosely bound (water-soluble) pectic substances. In the water-soluble fraction (WSF) of the peel samples, uronic acids are the predominant monomers. On the contrary, rhamnogalacturonan-I type neutral sugars, and especially arabinose and galactose, contribute equally, as compared to uronic acid, to the WSF of the pulp samples. Despite the low average DM value of pulp and peel pectin, pectic substances in both samples showed affinity for antibodies with different specificities indicating that a wide range of epitopes, including long blocks of unesterified galacturonic acids (GalA) residues as well as (short) blocks of esterified GalA residues, are present. No large differences between the pectic substances among the different dragon fruit varieties were observed