Effects of cooking and drying on phenolic compounds and antioxidant activity of African green leafy vegetables

Phenolic compounds play a significant role in our diets due to their proposed health benefits in the human body. Their presence in plants has therefore led to the increase in recognition of underutilized African green leafy vegetables (ALVs) as vital contributors to the food supply, which in itself is a component of food security in Africa. However, most ALVs are cooked prior to consumption or dried for preservation purposes. Cooking and drying of ALVs may induce chemical and physical changes to ALVs, thus affecting their phenolic composition and resultant health promoting properties. This review, therefore, aims to elucidate the several effects exerted upon ALV’s phenolic composition and antioxidant activity as a result of cooking and drying as well as a brief discussion on the health benefits correlated with ALV consumption.     

Nitrate-N determination in leafy vegetables: Study of the effects of cooking and freezing

Nitrate upon reduction to nitrite can cause methaemoglobinaemia or act as precursor in the endogenous formation of carcinogenic nitrosamines. The leafy vegetables are the major vehicle for the entry of nitrate into the human system. The present study was conducted to establish a flow injection analysis (FIA) technique to investigate the nitrate-N contents of four commonly consumed fresh leafy vegetables (Chinese cabbage, celery, lettuce and English cabbage) from market in Fiji. Two extraction techniques (activated carbon and alkaline extraction) were assessed to extract nitrate-N and the activated carbon extraction was preferred over alkaline extraction and applied. The recoveries of spiked nitrate-N in vegetable matrices ranged from 90.40% to 112.80% in activated carbon extraction with an average of 100.62%. The effects of cooking (boiling, baking and frying) and deep-freezing on the nitrate-N contents were also studied. Nitrate contents in selected leafy vegetables were determined by FIA coupled with Greiss protocol involving sulfanilamide and N-(1-naphthyl)ethylenediamine dihydrochloride as color reagents. Nitrate was determined in the linear range from 1.0 to 20.0 mg L⁻¹ with the method detection limit of 0.042 mg L⁻¹ (0.34 mg kg⁻¹). The results of the study show that nitrate contents in fresh leafy vegetables ranged from 1297 to 5658 mg kg⁻¹. Boiling reduces nitrate content by 47–56% whereas frying in Soya bean oil elevates nitrate content by as much as 159–307%. No significant change was observed in nitrate content after baking. The deep-freezing of the selected leafy vegetables shows that nitrate-N content fluctuates slightly from the original nitrate-N values over the seven day period. The FIA throughput was 38 samples h⁻¹.     

In vitro accessibility of β‐carotene from cooked Sri Lankan green leafy vegetables and their estimated contribution to vitamin A requirement

Vitamin A deficiency is an important issue for public health in Sri Lanka, where pro‐vitamin A carotenoids from green leafy vegetables provide most of the dietary vitamin A. The objective of this study was to analyse the β‐carotene content of seven types of green leafy vegetables and calculate the contribution of one traditionally cooked portion to the recommended daily allowance (RDA) of retinol. The total amount and in vitro accessibility of β‐carotene were determined using HPLC. The in vitro method simulates the conditions in the human intestinal tract. The all‐trans‐β‐carotene content in the fresh blanched vegetables ranged from 149 µg g^?1 dry weight (DW) in leaves of Alternanthera sessilis (mukunuwanna) to 565 µg g^?1 DW in Amaranthus caudatus (thampala). One portion (100 g) of green leaves cooked without fat (coconut) only contributed from 140 to 180 µg mg^?1 of the recommended daily allowance. A. sessilis, Centella asiatica (gotukola), Spinacea oleracea (nivithi) and A. caudatus, cooked with coconut fat contributed 140–680 µg mg^?1. However, stir‐fried or ‘malluma’ preparations (with coconut products) of Sesbania grandiflora (kathurumurunga) and Manihot esculenta (manioc) may provide more than 1.59–4.37 times the RDA of retinol. These results show that not only the choice of green leaves used but also the addition of fat while cooking is of great importance. Copyright © 2005 Society of Chemical Industry     

我国食品安全问题产生的原因及对策

目前,食品安全已成为全球性的重大战略性问题,随着我国国民经济的高速发展及人民生活水平的提高,对食品安全提出了越来越高的要求,解决食品安全问题对我国有重要的意义。在提出对食品安全和安全食品正确认识的基础上,从食品供应的各个环节具体分析了我国食品安全问题产生的因素,并提出以下相应对策:建立和完善相关的法律、法规及标准;加强食品安全的监督管理,加强食品安全重大关键技术的研究和开发,运用信息技术建立食品安全信息管理体系,建立食品安全社会信用体系,提高全民对食品安全的重视程度。     

发酵果蔬的功能及应用现状

随着消费者对健康饮食的日益重视,具有保健作用的发酵果蔬汁相关产品引起了研究者的广泛关注。果蔬是微生物生长的理想基质,果蔬汁发酵后会产生丰富的营养物质和多种功能活性,因此实现了果蔬高值化利用,使得未来发酵果蔬汁系列产品有着广阔的应用市场。本文综述了果蔬汁的常见发酵方式,发酵后的生物活性成分、功能活性以及发酵对果蔬汁的品质改善作用,对发酵果蔬汁行业的发展具有一定的指导意义。     

传统发酵豆制品营养功能成分研究进展

传统发酵豆制品主要包括腐乳、豆豉、豆酱和酱油等。 与未发酵豆制品相比,传统发酵豆制品在发酵过程中产生新的功能性 物质,不仅风味独特、易于消化吸收,而且在营养保健等方面更具优势。 该文从传统发酵豆制品的营养功能成分、活性以及发酵豆制 品食用安全等方面进行综述,旨在促进深入研究发酵豆制品中活性物质种类与结构,并为发酵豆制品生产工艺优化和食用安全提供 参考。     

Critical evaluation of the extrapolation of data relative to antioxidant function from the laboratory and their implications on food production and human health: a review

The use of the word ‘antioxidant’ has become widespread in food science, nutrition and consumer language, having become associated with potential health benefits linked to consuming sources of antioxidants in our food supply. However, there is significant doubt about direct antioxidant effects on human health. This may partly relate to methodology used for assessing functionality and activity (both in food matrices and in human health) as well as how data is extrapolated with respect to health based on laboratory analyses. In this review, the purpose and impact of antioxidants in food systems and on human health will be discussed, along with highlighting the best current methodology for analysing antioxidant effects. Consideration will also be made with respect to recommendations of how antioxidant activity should be reported, with a focus on being both scientifically accurate as well as minimising the risk of unwarranted extrapolations of benefits which might mislead end consumers.     

Provitamin‐A and xanthophyll carotenoids in vegetables and food grains of nutritional and medicinal importance

This study reports carotenoid composition of vegetables (n = 56), cereals (n = 12), pulses and legumes (n = 12), analysed by HPLC. It was hypothesised that food grains, like vegetables may be good sources of carotenoids. Amongst vegetables, higher level (mg/100 g dry weight) of lutein (210–419) was detected in green/red/capsicum and yellow zucchini, whilst zeaxanthin was dominant in kenaf (4.59). β‐Carotene (mg/100 g dry weight) was higher in green capsicum and kenaf (48,159) whilst carrot, ivy gourd and green capsicum contain α‐carotene (22–110). Amongst food grains, chickpea, split red gram and flaxseed contain higher levels (μg/100 g dry weight) of lutein (185–200) whilst zeaxanthin level was highest in puffed chickpea (1.8). Red unpolished parboiled rice was richest (μg/100 g dry weight) in β‐carotene (67.6) whilst whole black gram contained higher levels of α‐carotene (52.7). Thus, results indicate that chickpea and red unpolished parboiled rice are good sources of carotenoids. These carotenoid‐rich vegetables and grains may be exploited to meet the lutein and β‐carotene requirement.     

Nonthermal physical technologies to decontaminate and extend the shelf-life of fruits and vegetables: Trends aiming at quality and safety

Minimally processed fruits and vegetables are one of the major growing sectors in food industry. This growing demand for healthy and convenient foods with fresh-like properties is accompanied by concerns surrounding efficacy of the available sanitizing methods to appropriately deal with food-borne diseases. In fact, chemical sanitizers do not provide an efficient microbial reduction, besides being perceived negatively by the consumers, dangerous for human health, and harmful to the environment, and the conventional thermal treatments may negatively affect physical, nutritional, or bioactive properties of these perishable foods. For these reasons, the industry is investigating alternative nonthermal physical technologies, namely innovative packaging systems, ionizing and ultraviolet radiation, pulsed light, high-power ultrasound, cold plasma, high hydrostatic pressure, and dense phase carbon dioxide, as well as possible combinations between them or with other preservation factors (hurdles). This review discusses the potential of these novel or emerging technologies for decontamination and shelf-life extension of fresh and minimally processed fruits and vegetables. Advantages, limitations, and challenges related to its use in this sector are also highlighted.     

Native casein micelles as nanocarriers for β‐carotene: pH‐and temperature‐induced opening of the micellar structure

To apply native casein micelles (CM) as nanocarriers for lipophilic substances in non‐ or low‐fat food products, they have to be conditioned before loading. In this study, an experimental set‐up for the production and loading of CM was developed. Microfiltration was used to separate CM from skimmed milk. To identify optimal loading conditions temperatures (2, 20, 40 °C), pH values (6.8 and 5.5) and holding times (5, 15, 30, 60 min) were varied. The release of calcium, phosphate and protein from the micellar phase as well as static light scattering and transmission electron microscopy showed that CM were optimally primed at 2 °C and a pH of 5.5 for 5 min. Therefore, loading with β‐carotene was performed under those conditions. After the back‐extraction of β‐carotene, the photometrical analyses revealed total recovery rates of >79% whereby 94% of it was associated with the native CM.     

Effects of processing sorghum and millets on their phenolic phytochemicals and the implications of this to the health‐enhancing properties of sorghum and millet food and beverage products

Sorghum and millet grains are generally rich in phytochemicals, particularly various types of phenolics. However, the types and amounts vary greatly between and within species. The food‐processing operations applied to these grains, i.e. dehulling and decortication, malting, fermentation and thermal processing, dramatically affect the quantity of phenolics present, most generally reducing them. Thus the levels of phytochemicals in sorghum and millet foods and beverages are usually considerably lower than in the grains. Notwithstanding this, there is considerable evidence that sorghum and millet foods and beverages have important functional and health‐promoting effects, specifically antidiabetic, cardiovascular disease and cancer prevention, due to the actions of these phytochemicals. Also their lactic acid bacteria‐fermented products may have probiotic effects related to their unique microflora. However, direct proof of these health‐enhancing effects is lacking as most studies have been carried out on the grains or grain extracts and not the food and beverage products themselves, and also most research work has been in vitro or ex vivo and not in vivo. To provide the required evidence, better designed studies are needed. The sorghum and millet products should be fully characterised, especially their phytochemical composition. Most importantly, well‐controlled human clinical studies and intervention trials are required. © 2014 Society of Chemical Industry     

High‐throughput microbial bioassays to screen potential New Zealand functional food ingredients intended to manage the growth of probiotic and pathogenic gut bacteria

A spectrophotometric bioassay was used to screen selected food ingredients intended for development of functional foods designed to influence the growth of gut bacteria. Dose–response profiles displaying Δ_growth, the magnitude of deviation from growth of controls, were generated for probiotics Lactobacillus reuteri, Lactobacillus rhamnosus, Bifidobacterium lactis and pathogens Escherichia coli, Salmonella Typhimurium and Staphylococcus aureus. Ingredients were manuka honey UMF?20+(dose‐dependently increased probiotics and decreased pathogens); bee pollen (biphasic growth effects against all); Rosehips and BroccoSprouts^® (increased all dose‐dependently); blackcurrant oil (little effect) and propolis (inhibited all strains). Ingredients were also bioassayed in pairs to assess desirable or undesirable synergistic interactions. Observed synergies included manuka honey (predominantly desirable); rosehips or BroccoSprouts® (desirable and undesirable); blackcurrant oil (desirable) and propolis (tended towards synergies reinforcing its antimicrobial effects), collectively revealing a complex web of interactions which varied by ingredient and bacterial strain. Manuka honey was particularly effective at influencing gut bacteria. The surprising frequency of undesirable synergistic interactions illustrates the importance of pre‐testing potential ingredient combinations intended for use in functional foods.     

Pioneer studies in trace element contamination of the food chain: disregard of prior work risks re‐inventing the wheel

Current publications tend to make little reference to early work in their field. The study of the contamination of the food chain by trace elements is no exception. It is suggested that among the reasons for the lack of early citations are the reliance on library databases, the need to keep lists of references concise, and increased specialisation. The contributions of the main pioneers are reviewed together with the principal areas of early investigation, namely trace elements in urban gardens, non‐ferrous metal‐mining spoil, sewage sludge and from atmospheric deposition. An outline is given of the development of the analytical methods that allowed accurate and rapid determination of trace elements. It is concluded that the disregard of the early period work results not only in its omission from university courses but in repetition of research. © 2000 Society of Chemical Industry     

Changes in the chemical composition of traditional Chinese‐type soy sauce at different stages of manufacture and its relation to taste

Chemical composition of traditional Chinese‐type soy sauce (TCSS) at different stages of manufacture (moromi fermentation and pasteurisation) were analysed. Results showed that total nitrogen, formaldehyde nitrogen, total titratable acid, reducing sugar, NaCl, water soluble peptides, free amino acids (FAAs) and Maillard reaction products in TCSS changed significantly during manufacture. Most of FAAs were released during initial stage (0–15 days) of moromi fermentation, peptides (1–5 kDa) kept dominant (69.34–80.88%) among all peptides during manufacture and Maillard reaction products increased progressively during moromi fermentation and increased sharply during pasteurisation. According to hierarchical cluster analysis and sensory evaluation, there were obvious correlation between FAAs and sensory score of over‐all in TCSS during manufacture, which indicated that balanced FAAs composition might be mainly responsible for the taste formation of TCSS. Besides, pasteurisation can further improve the over‐all taste of TCSS.