Ulf Svanberg

Estimation of carotenoid accessibility from carrots determined by an in vitro digestion method

Objective: To develop an in vitro digestion method to assess the impact of heat treatment, particle size and presence of oil on the accessibility (available for absorption) of α- and β-carotene in carrots.Design: Raw and cooked carrots were either homogenized or cut into pieces similar to chewed items in size. The carrot samples, with or without added cooking oil, were exposed to an in vitro digestion procedure. Adding a pepsin–HCl solution at pH 2.0 simulated the gastric phase. In the subsequent intestinal phase, pH was adjusted to 7.5 and a pancreatin–bile extract mixture was added. Carotenoids released from the carrot matrix during the digestion were extracted and quantified on high-performance liquid chromatography (HPLC).Results: Three percent of the total β-carotene content was released from raw carrots in pieces. When homogenized (pulped) 21% was released. Cooking the pulp increased the accessibility to 27%. Addition of cooking oil to the cooked pulp further increased the released amount to 39%. The trends for α-carotene were similar to those for β-carotene.Conclusion: The described in vitro digestion method allows a rapid estimation of carotene accessibility in processed carrots, which may reliably predict in vivo behavior.Sponsorship: This study was supported by the Swedish International Development Cooperation Agency (SIDA) and the International Program in the Chemical Sciences (IPICS), Uppsala University, Sweden.

In vitro accessibility of carotenes from green leafy vegetables cooked with sunflower oil or red palm oil.

Although vegetables and fruits are readily available and consumed in most areas of Tanzania, vitamin A deficiency is still prevalent. The objective of the present study was to measure the in vitro accessibility (available for absorption) of α-carotene and β-carotene in vegetable relishes prepared with or without oil. Derived results were used to calculate the contribution of vegetable relish to recommended daily intake of retinol. Five sundried green leafy vegetables from Tanzania were cooked without oil, with sunflower oil or with red palm oil. The total amount and in vitro accessibility of α-carotene and β-carotene from a portion (100 g) of vegetable relish was determined. The in vitro method used simulated the digestion process in the gastrointestinal tract. Carotenoids released after digestion were quantified using high-performance liquid chromatography. The total amount of β-carotene varied between 1211 and 3659 μ g/100 g among the five vegetable sources studied. From green leaves cooked without oil, 8-29% of the β-carotene content became accessible after in vitro digestion and 39-94% from leaves cooked with sunflower oil or red palm oil. Adding red palm oil instead of sunflower oil resulted in about twice as much accessible β-carotene, due to the high accessibility of its β-carotene content. The red palm oil contributed also a considerable amount of α-carotene. The results showed that by eating vegetable relishes with added oil daily, it should be possible to provide the recommended intake level of vitamin A.

Effect of oxygen and fluorescent light on the quality of orange juice during storage at 8°C

Abstract The effect of oxygen and light exposure and the combination of these two parameters on the retention of ascorbic acid, occurrence of non-enzymatic browning and the formation of 5-hydroxymethyl-2-furfuraldehyde (HMF) and furfural was investigated in orange juice stored at 8°C for 52 days. Orange juice, reconstituted and HTST-pasteurised, was stored in glass containers, covered on the sides with aluminium foil and sealed on the top with packaging materials, i.e. glass, polyethylene and paper carton. having different light transmission and oxygen permeation characteristics. The ascorbic acid content was significantly affected by the level of dissolved oxygen in the juice, but no effect of light could be observed under the conditions of this study. Browning increased during the first 3 weeks of storage in all samples and was over the whole period of storage significantly correlated to the level of dissolved oxygen, but the effect of light was insignificant. HMF and furfural content did not increase significantly in any of the samples during the 52-day storage at 8°C.

Inhibited growth of common enteropathogenic bacteria in lactic-fermented cereal gruels.

A natural lactic fermentation of mixtures of water and whole flour of either maize or high-tannin sorghum was obtained either before or after cooking to a weaning gruel: The preparations had a final pH of about 3.8 (range 3.67 to 4.00) and a ratio of lactic acid to acetic acid of 9∶1 (w/w). The growth of added (about 107 c.f.u./g gruel) Gram-negative intestinal pathogenic bacteria, enterotoxigenicEscherichia coli, Campylobacter jejuni, Shigella flexneri andSalmonella typhimurium, was strongly inhibited in the sour gruels, and the effect could primarily be explained by the low pH caused by the formation of lactic and acetic acids during the fermentation process. Of the added Gram-positive bacteria,Bacillus cereus andStaphylococcus aureus showed similar inhibited growth up to 7h after inoculation in the sour gruels. The strain ofStaphylococcus, however, showed only a continued reduction in growth in the fermented gruel samples, which had a viable lactic bacteria culture indicating the presence of a bacteriocin. This implies that a low pH (< 4.0) alone is not sufficient to sustain the inhibition of the growth ofStaphylococcus aureus. The survival studies were carried out at optimal temperatures for each respective enteropathogen.

Fermentation and nutrient availability

Abstract Malnutrition and deficiency of micronutrients are highly prevalent and even increasing in parts of several developing countries. Factors of immediate and direct influence to these nutritional disorders are inadequate food consumption and diseases, which usually interact in a mutually reinforcing manner. In addition, the bioavailability of many nutrients in vegetable diets is usually low, and this will significantly contribute to the nutritional inadequacy. To improve the nutrient intake, food preparation technologies have been advocated that will effectively increase the nutrient availability of vegetable diets. These technologies must, however, be simple, easily understood and culturally acceptable, and the food products must be affordable, in terms of economy and labour input. Several such traditional food technologies exist at household level in many developing countries, and include soaking, germination and fermentation. This paper will discuss the merits of the fermentation technique in order to improve the nutritional value of vegetable foods.

Processing of tomato: impact on in vitro bioaccessibility of lycopene and textural properties

BACKGROUND Human studies have demonstrated that processing of tomato can greatly increase lycopene bioavailability. However, the difference between processing methods is not widely investigated. In the current study different thermal treatments of tomato were evaluated with regard to their impact on in vitro bioaccessibility and retention of lycopene and beta-carotene as well as textural properties. Thermal treatments used were low (60 degrees C) and high (90 degrees C) temperature blanching followed by boiling. RESULTS Lycopene was relatively stable during thermal treatment, whereas beta-carotene was significantly (P < 0.05) reduced by all heat treatments except for low temperature blanching. In vitro bioaccessibility of lycopene was significantly increased from 5.1 +/- 0.2 to 9.2 +/- 1.8 and 9.7 +/- 0.6 mg kg(-1) for low and high temperature blanching, respectively. An additional boiling step after blanching did not further improve lycopene bioaccessibility for any treatment, but significantly reduced the consistency of low temperature treated samples. CONCLUSION Choice and order of processing treatments can have a large impact on both lycopene bioavailability and texture of tomato products. Further investigations are needed, but this study provides one of the first steps towards tomato products tailored to optimise nutritional benefits.

Inhibition of different strains of enteropathogens in a lactic-fermenting cereal gruel

Twenty-eight strains of enteropathogens, including Campylobacter, Salmonella, Shigella, enterotoxigenic Escherichica coli (ETEC), Staphylococcus and Bacillus were added to cereal gruels prepared from low-tannin sorghum and inoculated with a lactic acid starter culture. Campylobacter strains were not detectable after 6 h, and Salmonella, Shigella and Staphylococcus strains not after 12 h. No viable cells of Bacillus strains were detected after 16 h of fermentation and the ETEC strains were completely inhibited after 24 h. No strain variability was observed within the different genera. In control gruels (no starter culture added), all the enteropathogens increased in number during incubation at 32°C except for the Campylobacter strains which decreased after 12 h of incubation.

pH and acidity in lactic-fermenting cereal gruels: effects on viability of enteropathogenic microorganisms

Survival of Bacillus cereus, Campylobacter jejuni, enterotoxigenic Escherichia coli, Salmonella typhimurium and Shigella flexneri during lactic acid fermentation of cereal gruels prepared from low-tannin (white) and high-tannin (red) sorghum varieties was studied. A previously fermented gruel (starter culture, SC) recycled daily or stored for 7, 14 or 28 days, germinated cereal flour (power flour, PF), or a combination of PF and SC (PF+SC) were used as starters. At 24 h, the pH of all gruels with added starter was ≤4; the pH in control gruels without starter was ≥5.2. pH decrease was significantly faster in gruels made with PF+SC than with either PF or SC alone (P<0.05). A daily recycled SC resulted in a significantly faster decrease in pH (P<0.05) than SC stored for more than 7 days. Acid production was correlated with pH decrease (r=−0.94; P<0.01). In control gruels, the enteropathogens remained at the inoculation level or increased in number. Their growth was inhibited within 24 to 48 h in the fermented gruels, in the order: Bacillus > Campylobacter > Escherichia coli > Salmonella > Shigella. The inhibition rate was significantly faster in fermenting gruel with PF+SC (P<0.05) than in gruel with PF or SC alone and correlated with pH development (r=0.71; P<0.01). Both white and red sorghum gruels gave similar results. Using PF+SC as a starter resulted in a faster decrease in pH as well as a more rapid inhibition of enteropathogenic microorganisms. The effect is optimal if the SC is transferred daily.

Processing of quinoa (Chenopodium quinoa, Willd): effects on in vitro iron availability and phytate hydrolysis

The effect of different processing techniques was studied on in vitro iron availability and phytate hydrolysis in high and low saponin content quinoa (Chenopodium quinoa, Willd) seeds. Water slurries of ungerminated and germinated quinoa flour were processed by cooking, soaking, and fermentation using Lactobacillus plantarum as starter. Iron solubility under physiological conditions (in vitro) was measured and used as an estimation of iron availability. Phytate (inositol hexaphosphate/IP6) and its degradation products were analysed by an HPLC method. The IP6 + IP5 content was reduced by cooking with 4 to 8%, germination with 35 to 39%, soaking with 61 to 76% and by fermentation with 82 to 98%. The highest reduction, about 98%, was obtained after fermentation of the germinated flour. Cooking had no effect on the amount of soluble iron. Iron solubility increased, however, two to four times after soaking and germination, three to five times after fermentation and five to eight times after fermentation of the germinated flour samples and was highly correlated to the reduction of IP6 + IP5 (P < 0.001). There was no difference between the quinoa varieties with regard to phytate reduction and iron solubility. The pH in fermented samples was reduced from 6.5 to about 3.5, due to lactic acid formation.

In Vitro Bioaccessibility of β-Carotene from Heat-Processed Orange-Fleshed Sweet Potato

Orange-fleshed sweet potato (OFSP) is currently promoted in parts of sub-Saharan Africa as a biofortified staple food with large potential to provide considerable amounts of provitamin A carotenoids. However, the bioaccessibility of provitamin A carotenoids from OFSP has not been widely investigated, especially not as an effect of different preparation methods. In this study, we used an in vitro digestion model to assess the bioaccessibility of beta-carotene from differently heat-processed OFSP. The fraction of carotenoids transferred from the food matrix to a micellar phase obtained after microfiltration and to a supernatant obtained after low-speed centrifugation was investigated. The percentage of accessible all-trans-beta-carotene in the micellar phase varied between 0.5 and 1.1% in the heat-processed OFSP without fat and between 11 and 22% with the addition of 2.5% (w/w) cooking oil. In comparison with the micellar phase, the percentage of accessible all-trans-beta-carotene in the supernatant phase was significantly higher (P < 0.001), between 24 and 41% without fat and between 28 and 46% with fat. These results support the importance of fat for an improved micellarization of beta-carotene. Overall, the high in vitro bioaccessibility of beta-carotene from heat-processed OFSP indicates that sweet potato might be a promising dietary approach to combat vitamin A deficiency.