Soft-rot Resistance of Coloured Potato Cultivars (<Emphasis Type="Italic">Solanum tuberosum</Emphasis> L.): The Role of Anthocyanins

Coloured potatoes (Solanum tuberosum L.) rich in anthocyanins are gaining increasing interest on the markets, mainly due to beneficial health effects. Potato varieties containing colour pigments are therefore utilized more and more in actual breeding programmes. In this study, 10 purple-fleshed potato cultivars were compared in their resistance to soft rot caused by Pectobacterium carotovorum (Pc) with 10 white/yellow-fleshed potato cultivars. The results revealed that coloured potato cultivars exhibited on average better resistance to soft rot than white/yellow-fleshed potato cultivars. On tuber halves of purple-fleshed cultivars, the extent of rotting caused by Pc was on average 28.6% lower than on white/yellow-fleshed cultivars. The greater resistance of coloured potatoes coincided with the presence of anthocyanins, higher concentrations of soluble phenols and elevated polyphenol oxidase activity in tuber tissue. These three components were significantly correlated with the extent of rotting caused by Pc. However, coloured and white/yellow-fleshed cultivars were not very different in phenylalanine ammonia-lyase and peroxidase activity. There were also no significant differences in concentrations of dry matter, starch, crude protein and glycoalkaloids. Key findings reveal that total soluble phenols and anthocyanins contributed crucially to resistance expression in tuber tissue of coloured potato cultivars.     

Mechanical and physical properties of expanded starch, reinforced by natural fibres

Biodegradable foams made from potato starch and natural fibres were obtained by extrusion. The effects of varying origins of these fibres on foam properties were studied, as well the relationships between their properties and the foam microstructure. The addition of fibres increased the expansion index and led to a significant reduction in water adsorption of starch foams, generally improving foam properties. The mechanical properties of the foams were affected by both relative humidity (RH) of storage and foam formulation. In general, as the RH increased, the foam strength decreased. The formulation presenting the best mechanical properties contained 10 wt% hemp fibre and had a maximal resistance of 4.14 MPa and a modulus of 228 MPa, corresponding to a more compact and dense microstructure.     

The role of the gluten network in the crispness of bread crust

Crispness features of baked products strongly determine consumer acceptability. For many baked products, such as bread, the outer crust gives the crispy sensation. Confocal scanning laser microscopy of the structure of bread crust revealed a continuous protein phase and a discontinuous non-gelatinized starch phase in the outer crust. In contrast, the crumb and inner crust, showed a gelatinized starch network associated with a protein network. The role of the protein phase of the outer crust in determining crispness has been studied. During storage, the crispness of bread crust alters as a result of changes in water content/activity resulting from moisture redistribution within the bread and between the bread and its environment. Water content was affected by the flour protein content and by selectively modifying the crust protein phase of a model bread with enzymes, as well as by storing breads at high and low relative humidity (80–40% RH). Protease modification resulted in a lower water content and activity in the crust during the first hours of storage. In contrast, modification by transglutaminase had the opposite effect and gave rise to higher water retention of the crust compared to the un-treated d bread. This shows that modification of the protein network can be used to regulate the water holding capacity of the crust. Sensory analysis confirmed the retention of crispness in protease modified bread crust after 2 h storage at 80% RH conditions, whereas both the untreated and transglutaminase-treated breads lost their crispness. A negative relationship between water activity/content and crispness was found. Modification of the starch phase of the crust by alpha-amylase produced a bread crust with a low water activity. However, a steep increase in the water activity was observed after 2 h storage at 80% RH with a concomitant loss of crispness. These results indicate an important role of the gluten network in determining crust properties.     

Effect of germination time on physicochemical properties of brown rice flour and starch from different rice cultivars

The present work was designed to obtain information on the effect of germination time on the selected physicochemical properties of brown rice flour and starch prepared from three different rice cultivars. Changes in total starch, amylose and amylopectin contents of flour, amylopectin/amylose ratio and molecular weight of starch, gelatinization, pasting, rheological, and morphological properties of flour and starch during 5 days of germination were investigated. Significant changes of pasting and rheological properties of brown rice flour were found during germination, but only small changes of these properties could be found in isolated starch. Scanning electron micrographs of flour showed that the continuous matrix structure of flour was highly destroyed after germination and scanning electron micrographs of isolated starch showed that after three days of germination, pits and holes were discovered on the surface of some starch granules. Germination had little effect on the average molecular weight of starch, but the polydispersity value in germinated brown rice (2–5 days germination) was higher than that in non-germinated brown rice. The changes observed in physicochemical properties of brown rice flour and starch after germination provided a crucial basis for understanding flour and starch modification mechanisms with potential applications for an industrial scale.     

Effect of Different Defoliation Systems of Ryegrass–Clover on Yield and Selected Quality Parameters of Organic Potatoes (Solanum tuberosum L.) for Industrial Processing at Harvest and After Storage

The nitrogen supply plays an important role in achieving quality characteristics in organic potato farming. Different defoliation systems of ryegrass–clover may influence the amount of fixed nitrogen available to the tubers. In a field experiment, the effect of different defoliation systems (cutting, mulching and a combination of them) of the pre-crop ryegrass–clover on selected quality attributes of organically grown potatoes, destined for processing into French fries (cv. Agria) or crisps (cv. Marlen), were conducted in two consecutive years (2003 and 2004). Parameters studied included compounds related to the sensory properties of potato food (tuber dry matter, starch, reducing sugars) as well as nutritional quality (nitrogen, minerals). Selected agronomic parameters such as total tuber yields and tuber size distribution were also compared. Furthermore, the influence of additional slurry fertilisation and 4 months of storage on these parameters were investigated. Total yields and portion of tuber yield 50–60 mm were significantly affected by the pure mulching variant in 2003. In 2003, the starch concentration at harvest, as well as after storage, was above the required minimum of 22% (cv. Marlen) and 19% (cv. Agria), while in 2004, this was slightly beneath these values. In 2004, a significant increase of starch concentration by the pure cutting variant was observed. In both years, mulched ryegrass–clover caused a decrease in tuber DM contents of 2.10 and 3.54%, respectively, compared to the cutting systems. Fertilisation significantly decreased DM and starch concentration. In 2004, the reducing sugar concentration of tubers of cv. Marlen from the pure cutting system was with 2.1 g kg^?1 FM above the required maximum of 1.5 g kg^?1 for crisps. In addition, storage led to a three to fivefold increase of reducing sugars concentrations in the tubers in this year. After slurry fertilisation, 8.8% higher N contents and up to 36% higher K concentrations were measured. Mulching of the pre-crop combined with slurry application led to an up to 61% higher tuber K concentration compared to the cutting system. The results indicate that different defoliation systems of the pre-crop ryegrass–clover and slurry fertilisation had only minor effects on internal tuber quality attributes. Quality parameters were more affected by the prevailing weather conditions in combination with the genotype of different potato cultivars.     

施氮量对糯小麦和非糯小麦籽粒淀粉组分与理化特性的影响

为探明氮肥对小麦籽粒淀粉组分和理化特性的影响,采用田间试验,分析了4个施氮量(0、100、200、300kg·hm~(-2))对糯小麦(农大糯50222)和非糯小麦(轮选987)籽粒淀粉组分与理化特性的影响。结果表明,随施氮量的增加,小麦籽粒淀粉含量降低,轮选987籽粒中B型淀粉粒的数目占比增加,而农大糯50222籽粒的B型淀粉粒数目占比呈减少趋势;增施氮肥能显著提高小麦籽粒淀粉的峰值黏度和谷值黏度。相同施氮量处理下,轮选987淀粉的被测糊化特征参数(除谷值黏度外)均大于农大糯50222。施氮量不同,2个品种籽粒淀粉X-衍射图谱中各峰的位置和相对强度明显不同。随施氮量的增加,轮选987淀粉的相对结晶度增大,而农大糯50222淀粉的相对结晶度减小。相关分析表明,小麦籽粒的直链淀粉含量和直支比与最终黏度、稀澥值、反弹值、糊化温度和峰值时间呈显著正相关,与谷值黏度和相对结晶度呈显著负相关;支链淀粉含量反之。小麦籽粒的B型淀粉粒数目占比与峰值黏度、稀澥值呈显著负相关。综上所述,施氮量可影响小麦籽粒的淀粉含量和粒度分布,进而改变其糊化特性和晶体特征。     

温度对马铃薯α淀粉老化的影响

采用挤压膨化技术制作马铃薯α淀粉,并利用酶水解法及X-射线衍射法等研究了在同一贮藏时间内,不同贮藏温度对膨化马铃薯α淀粉老化变化的影响,探讨了影响机理。研究结果表明,贮藏温度从23℃±1℃降低到-18℃±1℃时,贮藏期为180d的样品α度也从87.8%明显降低到80.2%,样品的结晶度从8.4%上升为16.45%;说明样品α度的高低与贮藏温度的高低成正比,而样品的老化程度高低与贮藏温度的高低成反比。     

Blue Maize: Morphology and Starch Synthase Characterization of Starch Granule

The use of pigmented maize varieties has increased due to their high anthocyanins content, but very few studies are reported about the starch properties of these grains. The aim of this work was to isolate the starch granules from pigmented blue maize and carry out the morphological, physicochemical, and biochemical characterization studies. The proximate composition of starch granules showed high protein contents, after purification, the blue maize starch presented lower protein amount than starch from white maize (control). Although the purity of starch granules was increased, the damaged starch (determined for the Maltase cross absence) was also increased. Scanning electron microscopy showed the presence of some pores and channels in the blue maize starch. The electrophoretic protein profiles showed differences in the bands that correspond to the enzymes involved in the starch biosynthesis; these differences could explain the variation in morphological characteristics of blue maize starches against starch from white maize.     

Starch Characteristics of Modern and Heirloom Potato Cultivars

In a number of ways, modern potato breeding efforts differ from those that created heirloom cultivars. As a result of the rapid expansion of the potato processing industry in the mid twentieth century, potato breeders shifted their focus from fresh market varieties to those intended for the fry and chip markets. Selection for higher dry matter content and lower reducing sugar levels in tubers was successful. This study sought to determine whether modern processing cultivars differ from heirloom cultivars for two major characteristics of tuber starch, amylose content and starch granule morphology. Since breeding efforts for processing potatoes have focused on the maintenance of tuber quality during storage, these parameters were measured in both fresh and stored tubers. Twenty cultivars selected to span the range of cultivar release dates in the U.S. were grown at Hancock, WI in 2009 and 2010 and evaluated for tuber amylose content and measurements of starch granule surface area, length, width, length to width ratio, and smoothness. These traits were found to be stable across years and during storage. Significant differences in the amylose content and starch granule morphology exist among cultivars, but there is no clear distinction between modern and heirloom cultivars. Genetic variation for amylose content and starch granule morphology was found within the set of clones sampled for this study. However, germplasm with higher amylose content will need to be identified and utilized in breeding if the nutritional benefits associated with high fiber and low glycemic index are to be realized.     

马铃薯氮素的吸收、积累和分配规律

植株体内氮素浓度的高低反映了其生长势的强弱,马铃薯生育期间各器官氮素浓度的变化始终表现为叶片>地上茎>块茎,叶片中的氮素浓度高低反映了叶片光合活性的大小。马铃薯对氮的吸收与营养生长和块茎的增长密切相关,植株对氮的需求量受其生长状况所控制。而且,氮在植物体内很容易流动,块茎形成后,大量的氮素转移到块茎中,用于块茎的建成和营养贮存。马铃薯植株在淀粉积累开始后,各器官中氮素加快了向块茎的转移,使叶片和地上茎的衰老进一步加剧。因此,在马铃薯高产栽培实践中,须注重氮、磷、钾的适量与配合施用,使之既能满足块茎的形成与生长的需要,又可防止植株生长过旺或后期发生早衰。本试验表明,在因素中量(适量)组合下,每生产500kg块茎需要纯N2 65kg。     

Biochemical and molecular control of cold-induced sweetening in potatoes

The benefits of being able to process potatoes directly into chips or fries from cold storage (2 to 4 C) include less shrinkage, retention of dry matter, decreased disease loss, extended marketability, and the elimination of the need for dormancy-prolonging chemicals. Unfortunately at low temperature, potato tubers undergo a phenomenon known as cold-induced sweetening where the rate of conversion of starch to reducing sugars (i.e., glucose and fructose) is accelerated. As raw potatoes are sliced and cooked in oil at high temperature, the accumulated reducing sugars react with free amino acids in the potato cell forming unacceptably brown- to black-pigmented chips or fries via a non-enzymatic, Maillard-type reaction. Potatoes yielding these unacceptably colored products are generally rejected for purchase by the processing plant. All commercial potato cultivars presently used for the production of potato chips and fries accumulate excess free reducing sugars when exposed to cold stress. If a “cold-processing potato” was available, energy savings would be realized in potato-growing regions where outside storage temperatures are cool. In regions where outside temperatures are moderately high, increased refrigeration costs may occur. This expense would be offset, however, by removal of the need to purchase dormancy-prolonging chemicals, by a decreased need for disease control and by improvement of long-term tuber quality. The primary goal of this review is to describe recent research of a biochemical and molecular nature that relates to the underlaying mechanisms regulating post harvest, cold-induced sweetening in potato tubers. No attempt was made to outline the extensive research conducted on the genetic manipulation of carbon metabolism between starch and free sugars during photosynthesis and/or during potato development in relation to source/sink interactions.     

Structure and Mechanics of Starch Bread

The mechanical properties of breads made of potato or wheat starch were measured in two successive compression/decompression cycles. From the shape of the stress–strain curves, the initial modulus and the critical stress and strain could be derived; the critical stress and strain are those at which the crumb structure starts to collapse. The magnitude of the stress–strain related parameters changed markedly during storage. The initial modulus, as well as the critical stress for structural collapse, increased, and the critical strain decreased. Moreover, the resistance of bread crumb to collapse of structure in compression decreased. The mechanical properties of potato starch bread changed more rapidly than those of wheat starch bread. The results are discussed in relation to the structure of the starch breads on different levels, i.e. from molecular (amylopectin recrystallisation) to macroscopic (sponge structure). It is concluded that the mechanical properties of the starch breads are determined by the mechanical properties of the condensed lamellae and beams consisting of irregularly shaped, partly swollen starch granules as well as by the distribution of the thickness of the lamellae and beams.     

Black currant polyphenols: Their storage stability and microencapsulation

Interest in the consumption of fresh fruits is, to a large extent, due to its content of bioactive nutrients and their importance as dietary antioxidants. There is a growing demand for delivery of antioxidants through functional foods with the related challenge of protecting their bioactivity during food processing and subsequent passage through the gastrointestinal tract. This study focuses on the evaluation of concentration of bioactive compounds in black currant berries (Ribes nigrum L.) and retention of black currant polyphenol compounds and their antioxidant activity after microencapsulation by spray-drying. The polyphenol contents and antioxidant activities were assessed for 5 black currant cultivars grown in Canada in fresh and stored fruits at −20 °C for 9 months. The Ben Alder cultivar was the richest in anthocyanins and flavonols content with high antioxidant potential measured with ABTS and DPPH radicals (4.5 and 2.4 mM/100 g). Black currant polyphenols were stable during 9 month of storage at −20 °C. The results of this study indicated that in black currants storage did not affect negatively the antioxidant capacity. The good stability of bioactive compounds of black currants during freezer storage allows prolonging the storage time of these berries. Maltodextrins with different DE (dextrose equivalent): DE11, DE18, DE21 and inulin were selected as wall material. The stability of encapsulated polyphenols during 12 months storage at 8 °C and 25 °C was evaluated. Compared to maltodextrins DE18 and DE21, maltodextrin DE11 had not only higher drying yield but also offered better protection for phenolics during storage. Radical scavenging activity studies demonstrated significant antioxidant activity of microencapsulated powders before and after storage. The black currant polyphenol microcapsules described in this study represent a promising food additive for incorporation into functional foods due to antioxidant content.     

Biochemical characterization of QTLs associated with endosperm modification in quality protein maize

Genetic analysis using quality protein maize (QPM) recombinant inbred lines derived from K0326Y QPM and W64Ao2 identified three quantitative trait loci (QTL) in bins 1.06, 7.02 and 9.03 associated with opaque2 endosperm modification. We evaluated the effects of these QTLs on protein accumulation and starch physicochemical properties. The QTL in bin 1.06 is close to α-zein genes, and vitreous individuals with this QTL had increased accumulation of 19-kDa α-zein, 27-kDa γ-zein and legumin-1. The QTL in bin 7.02 corresponds to the γ-zein locus, and greater accumulation of this protein was found in vitreous individuals. The QTL in bin 9.03 is close to starch biosynthetic genes; greater accumulation of granule-bound starch synthase and amylose was observed in vitreous kernel samples with this locus and that in bin 1.06, as well as less gelatinization enthalpy and crystallinity. Vitreous kernels contained angular-shaped/compact starch granules and more short-intermediate length chains of amylopectin. These results support that endosperm modification in QPM is associated with increased accumulation of γ-zein and other storage proteins, but also show that synthesis of less crystalline starch with more amorphous regions at the periphery of granules, which favor their packing and association with endosperm proteins, may also be an important factor.     

Rheology and texture of starch gels containing iodine

The objective of this study was to investigate the textural and rheological properties of starch gels containing different levels of iodine. The research goal is to understand the architectural organization of granules by utilizing iodine as a marker. Corn (CS), wheat (WS), potato (PS) and tapioca (TS) starch gels containing varying concentrations of iodine were prepared in a Rapid Visco Analyser (RVA). The gels were analysed by using a rheometer for small-deformation properties and also by using a texture analyser for large deformation properties following storage for 1 or 7 days. With increasing concentration of iodine, the firmness of gels decreased and the extent of decrease varied for the different starches. The extent of change in complex modulus (G*) of the gels was highest in the A-type starch, CS, but was different from WS, which is also an A-type starch. The G* for PS gels (B-type) decreased with the addition of 0.1% iodine but there was no significant difference upon increasing the iodine concentration. The G* for the C-type TS gels was lower than 15 Pa. These observations suggest a difference in the microstructure of the starch gels formed, likely resulting from differential leaching of polymers.     

Supplementing white maize masa with anthocyanins: Effects on masa rheology and on the in vitro digestibility and hardness of tortillas

The aim of this work was to supplement masa made from nixtamalized white maize flour (NWMF) with anthocyanins (0.0, 0.03, 0.06 and 0.12 g/100 g of masa), and to evaluate the effects on the rheological properties of the masa and on color, staling, in vitro digestibility, and hardness of tortillas. Tortilla baking reduced the content of anthocyanins by about 10%. The color parameters of the tortillas added with anthocyanins was similar to that of tortillas made with blue maize. Attenuated total reflection ATR-FTIR spectra showed that the 1022/1047 peak ratio increased, indicative that retrogradation increased with storage time, but the ratio was significantly lower for tortillas with added anthocyanins than without them, and lower for higher anthocyanins concentration. Freshly made tortillas added with anthocyanins exhibited lower ready digestible (about 35%) and slowly digestible (about 20%), but higher resistant (about 45%) starch fractions. Tortillas with 0.12 g of anthocyanins showed significantly lower hardness than the control tortillas (without added anthocyanins). Both previous mentioned effects can be associated with retrogradation, which on turn could be linked to anthocyanins-starch complexes and inhibition of amylolytic enzymes.     

Comparison of structural features of reconstituted doughs affected by starches from different cereals and other botanical sources

Starch, as the main component of flour products, determines the physicochemical properties of dough. This work investigated the relationship of the physical properties of seven types of starches from various cereals with the structural features of reconstituted dough. Results of mixing and tensile properties analysis and scanning electron microscopy displayed that rice reconstituted flour exhibited maximum water absorption; pea reconstituted flour had higher dough stability; sweet potato dough had higher tensile resistance; highland barley dough had the greatest extensibility. Moisture distribution analysis revealed that various model dough showed remarkably different water distribution, which was distributed at T₂₁ (0.07–0.11 ms), T₂₂ (0.8–2.66 ms) and T₂₃ (10.0–20.82 ms). Correlation analysis indicated that large starch granules associated with good dough stability; amylose content of starch positively affected tensile resistance of dough; crystallinity of starch showed negative effects on water absorption; starch with higher crystallinity associated with greater dough stability.     

Properties of starch-based foam formed by compression/explosion processing

Single-use foam packaging is used by manufacturers to protect and preserve a wide array of food and industrial products. Starch is one possible alternative material for making foam products. Starch-based foam was made using a compression/explosion process to study its properties and potential for single-use packaging. A feedstock was first prepared which consisted of wheat (WS), corn (CS) or potato starch (PS) that was formed into aggregates (1–3 mm) and conditioned to moisture levels ranging from 8 to 20%. The conditioned aggregates were loaded in an aluminum compression mold heated to 230°C and compressed for 10 s with 3.5 MPa force. The force was instantaneously released resulting in an explosive release of steam as the starch feedstock expanded and filled the mold. The moisture content of the feedstock influenced the density and compressive properties of the foam. Wheat, corn and potato starch feedstock with 17, 17 and 14% moisture content, respectively, produced foam with some physical and mechanical properties similar to those of commercial food containers. The starch foam had the general shape of the mold and appeared similar to polystyrene. The microstructure of the foam revealed a cellular structure with mostly closed cells less than 1 mm in diameter. However, some regions of the foam had a microstructure similar to that of expanded polystyrene except that the cells were much smaller (<0.1 mm).     

皮裸燕麦胚乳淀粉形态结构及理化性质的比较

燕麦作为血糖生成指数较低的食品,被广泛应用于食品、医药工业。为比较皮、裸燕麦胚乳淀粉理化性质的差异,探究皮、裸燕麦在食品等加工利用方面的不同,以2个裸燕麦品种(白燕2号,坝燕18)以及2个皮燕麦品种(蒙燕1号,塔娜)为材料,通过扫描电镜观察燕麦胚乳淀粉颗粒的形态,采用X-射线衍射分析(XRD)、傅里叶变换远红外光谱、以及¹³C固体核磁共振等方法研究淀粉的理化性质,同时测定其支链淀粉链长和淀粉的消化速率。研究结果表明,燕麦胚乳中淀粉同时以复粒淀粉和单颗粒淀粉形式存在,复粒淀粉在淀粉提取中易破裂,形成不规则的多面体颗粒,粒径多在5～8μm。4个燕麦品种胚乳的淀粉均为A型晶体,但膨胀势和溶解度存在差异,裸燕麦坝燕18膨胀势最高,溶解度最低。皮、裸燕麦在淀粉晶体结构方面存在差异,皮燕麦淀粉较裸燕麦有更高的结晶度和表层有序度,裸燕麦淀粉无定形比例和表观直链淀粉含量更高,导致皮、裸燕麦在食品加工方面的差异。皮、裸燕麦支链淀粉链长分布不同,裸燕麦的长支链分布少,慢速消化淀粉(SDS)含量高,尤其坝燕18的SDS含量明显高于其他三个品种,更适合作为减肥食品。