Effect of pretreatments and freezing rate on the firmness of potato tissue after a freeze–thaw cycle

The texture of potato tissue after a freeze–thaw process using different freezing rates and different pretreatments was analysed, in order to select the best strategy for optimum preservation of the textural characteristics of pre‐frozen potato. Ten blanching conditions were tested and a two‐step blanching process with calcium chloride (0.07 g mL^?1) proved the most effective in protecting the tissue after a freeze–thaw process (maximum load force around 10–55% of the raw tissue, depending on potato batch, for air‐blast freezing and 20–60% for immersion freezing). Vacuum impregnation at 100 and 400 mbar, even when followed by different pre‐drying treatments to remove excess water, was very detrimental to resistance to a freeze–thaw process (maximum load force below 10% of the raw tissue for air‐blast freezing and below 20% for immersion freezing). Microstructure analysis confirmed better tissue integrity retention with ethyleneglycol immersion freezing instead of air‐freezing. Differences were found between batches with a 6‐month difference in storage time, indicating that the fresher batch was more suitable for freezing.     

Enzymatic treatment of peanut kernels to reduce allergen levels

This study investigated the use of enzymatic treatment to reduce peanut allergens in peanut kernels as affected by processing conditions. Two major peanut allergens, Ara h 1 and Ara h 2, were used as indicators of process effectiveness. Enzymatic treatment effectively reduced Ara h 1 and Ara h 2 in roasted peanut kernels by up to 100% under optimal conditions. For instance, treatment of roasted peanut kernels with α-chymotrypsin and trypsin for 1–3 h significantly increased the solubility of peanut protein while reducing Ara h 1 and Ara h 2 in peanut kernel extracts by 100% and 98%, respectively, based on ELISA readings. Ara h 1 and Ara h 2 levels in peanut protein extracts were inversely correlated with protein solubility in roasted peanut. Blanching of kernels enhanced the effectiveness of enzyme treatment in roasted peanuts but not in raw peanuts. The optimal concentration of enzyme was determined by response surface to be in the range of 0.1–0.2%. No consistent results were obtained for raw peanut kernels since Ara h 1 and Ara h 2 increased in peanut protein extracts under some treatment conditions and decreased in others.     

Effects of blanching, freezing and freeze-drying on the fatty acid contents of green beans

GC-FID was used to monitor changes over time in palmitic, stearic, arachidic, oleic, linoleic and linoleic acid contents of green beans subjected to various preservation treatments. In beans stored in polyethylene bags at –22°C without prior blanching, all fatty acid contents dropped appreciably within the first month of storage, regardless of whether the beans had been hand- or vacuum-packed. In beans which had been freeze-dried then stored at room temperature in an airtight container, polyunsaturated fatty acid contents dropped appreciably only after 2 months.     

Effect of thermal treatment on glucosinolates and antioxidant-related parameters in red cabbage (Brassica oleracea L. ssp. capitata f. rubra)

The effects of various thermal processing treatments (blanching, boiling and steaming) of red cabbage, Brassica oleracea L. ssp. capitata f. rubra cv. ‘Autoro’, were assessed for the levels of glucosinolates (GLS), total phenols (TP), total monomeric anthocyanins (TMA), l-ascorbic acid (L-AA) and soluble sugars, as well as for the antioxidant potential by the ferric reducing ability power (FRAP) and oxygen radical absorbance capacity (ORAC) assays. Individual native GLS were determined by ion-pair HPLC-MS/DAD. There were significant (p < 0.05) losses in blanched red cabbage: TP, 43%, TMA 59%, FRAP 42%, ORAC 51%, L-AA 48% and soluble sugars 45%. Boiling gave less extensive reductions: TP 16%, TMA 41%, FRAP 17%, ORAC 19%, L-AA 24% and soluble sugars 19%. Steaming caused no losses for TP, ORAC, FRAP or soluble sugars. However, significant reductions were found for TMA and L-AA, with 29% and 11%, respectively. In general losses were accounted for in the processing waters; however, TMA was not fully recovered, indicating degradation. Total GLS were severely affected by processing, with reductions of 64%, 38% and 19% in blanched, boiled and steamed red cabbage, respectively. Total aliphatic and indole GLS were similarly affected. Lost GLS were partially recovered in the processing water.     

Structural modification by different pretreatment methods to enhance microwave-assisted extraction of β-carotene from carrots

Since the structure of a material is a key factor influencing the extraction efficiency, any means to modify the structure to enhance extraction is attractive. As limited information is available on the effect of sample pretreatment prior to extraction on the extractability of a bioactive compound, the effects of selected pretreatment methods, i.e., soaking in citric acid, blanching in water as well as in citric acid, on the sample structure and subsequent microwave-assisted extraction (MAE) were investigated; carrots and β-carotene (as well as carotenoids) were selected as the test material and bioactive compound, respectively. A suitable condition to extract β-carotene in terms of the microwave power and extraction time was determined. Comparison between MAE and Soxhlet extraction was also made. At the optimized condition the contents of β-carotene and total carotenoids extractable from carrots blanched in water (29.74 and 58.04 mg/100 g dry basis) and in citric acid (32.08 and 61.62 mg/100 g dry basis) were significantly higher than those from the untreated carrots (23.26 and 51.79 mg/100 g dry basis). The antioxidant activities of the extracts obtained from carrots blanched in water and in citric acid were also higher than that from carrots with no pretreatment. Comparison between MAE and Soxhlet extraction revealed that the extract from MAE contained lower amounts of β-carotene and total carotenoids and exhibited lower antioxidant activity; the required MAE time was significantly shorter, however.     

即食豆芽加工技术研究

本文对绿豆芽烫漂、保脆工艺条件进行了研究。研究结果表明：绿豆芽在0.15%柠檬酸水溶液中,90℃烫漂2.5min过氧化物酶完全失活、己醛含量明显降低;烫漂后在0.4?Cl2溶液中浸泡60min,豆芽脆度较好。     

Effect of pretreatment on surface topographical features of vegetables during drying

It is well recognized that many adverse changes occur to a food product during drying. Various pretreatment methods have thus been introduced to maintain the quality of the product. Among the various qualities, or properties, of a food product surface characteristics are one of the most important as these affect directly the consumer acceptance of the product. In terms of food safety surface characteristics may also be related to the attachment and hence thermal resistance of pathogenic microorganisms on the product surface. In this study attempt was made to investigate changes of the surface topographical features of vegetables as affected by pretreatment (blanching in hot water or soaking in 0.5-1.5% v/v acetic acid solution) and hot air drying (60 °C); cabbage and spring onion were selected as model vegetables to represent different natural topographical features of vegetables. An image analysis technique was used to monitor the changes of vegetable surfaces after pretreatment and during drying. The surface characteristic changes of vegetables were described quantitatively in terms of the relative roughness factor (R). It was observed that the surface characteristic changes, as affected by both pretreatment and drying processes, could be well monitored by the evolution of the R value.     

Analysis of volatile compounds in L. edodes blanched by hot water and microwave

The comprehensive flavour characterisation and volatile compounds of raw L. edodes, hot water blanching (HB) sample and microwave blanching (MB) sample were comparatively analysed by electronic nose technology and headspace solid‐phase micro‐extraction combined with gas chromatography‐mass spectrometry (HS‐SPME‐GC‐MS). Results indicated that volatile components in L. edodes markedly changed after HB and MB. Volatile compounds of raw L. edodes consisted mainly ketones, sulphide and alcohols, and 3‐octanone, as well as 1‐octen‐3‐one, were the major compounds. The content of ketones and sulphides in blanched samples markedly decreased, while the relative content of aldehydes, hydrocarbons and esters increased, which became the major volatile compounds of treatment samples. In addition, the percentage contents of esters, alcohols and sulphides in MB samples were significantly (P < 0.05) higher than that in HB samples, especially 1‐octen‐3‐ol, which contributes more to mushroom flavour. Therefore, MB is a better pretreatment method of L. edodes processing and cooking according to the results of experiment.     

The effect of blanching on quality attributes of dehydrated carrots during long-term storage

 The effect of blanching on the retention of β-carotene and ascorbic acid, and non-enzymatic browning (NEB) during storage of dehydrated carrot slices was studied. Blanched carrots contained higher β-carotene but lower ascorbic acid than their unblanched counterpart just after drying, whereas NEB was unaffected by blanching. During storage of dehydrated carrots a decrease in β-carotene and ascorbic acid content with an increase in NEB values was observed. Blanching was helpful in limiting the loss of quality parameters irrespective of storage and packaging conditions. Received: 22 May 2000 / Revised version: 11 October 2000     

Effects of some technological processes on glucosinolate contents in cruciferous vegetables

Effects of blanching, boiling and freezing of selected cruciferous vegetables (Brussels sprouts, white and green cauliflower, broccoli, and curly cale) on their glucosinolate (GLS) contents were determined. It was found that blanching and cooking of the vegetables led to considerable (P < 0.05) losses of total GLS, from 2.7 to 30.0% and from 35.3 to 72.4%, respectively. No systematic changes in total GLS were found in the vegetables that were blanched and frozen for 48 h. In addition, the highest concentration of cancer-protective compounds, such as aliphatic and indole GLS, were found in Brussels sprouts (sinigrin and glucobrassicin) and in broccoli (glucoraphanin).