Impact of wheat endogenous lipids on the quality of fresh bread: Key terms, concepts, and underlying mechanisms

Abstract

While wheat (Triticum aestivum L.) flour contains only low levels of lipids (2.0% to 3.0%), they tremendously affect fresh bread quality. They are either starch (30% to 40%) or nonstarch (60% to 70%) lipids. While the former are important in bread staling, they affect neither bread loaf volume nor crumb structure as they are only set free at the very end of the baking process and prior to that they are not available because of their location inside starch granules. This review mainly focuses on wheat nonstarch lipids and how they impact on bread quality. Traditional approaches for investigating their role in bread making have been to use flours varying in bread making quality, to defat and reconstitute flour with (fractions of) the extracted lipids and/or to supplement flour with lipids from wheat or other sources. More recently, lipases have been successfully applied to investigate how wheat lipids affect bread making. It is generally accepted that their impact on bread loaf volume and crumb structure largely if not entirely relates to that on bread dough gas cells stability. However, today there are still different views and hypotheses on the mechanism(s) whereby they impact fresh bread quality. This review first defines and introduces the key terms, concepts, and theories related to lipids, lipases, and bread making. Next, the effects that wheat endogenous lipids and their enzymatically released hydrolysis products have on fresh bread properties and the mechanisms whereby they exert these effects are reviewed. 2 LIPIDS 2.1 Definition and classification Lipids are an extremely diverse group of natural compounds for which no widely accepted definition exists. They exhibit greater structural variety than other classes of biological molecules (such as proteins and polysaccharides) and are similar only in that they are largely hydrophobic and only sparingly soluble in water (Voet,

Normal-Phase HPLC-ELSD to Compare Lipid Profiles of Different Wheat Flours

“…The predominant FAs present in non-starch lipids of the investigated flours were linoleic (60.9-65.3%), palmitic (19.5-20.4%) and oleic (10.7-14.1%) acids (Table 3). This is well in line with values reported in literature (50-65%, 19-26% and 10-21%, respectively) [3]. Furthermore, minor levels of α-linolenic, stearic and eicosenoic acid were detected.…”

“…This relative comparison per lipid class among different samples is possible because the investigated wheat flours do not differ (much) in their FA composition (Section 3.3). The most predominant wheat flour non-starch lipids reported in literature are TAGs (21-47%), digalactosyldiacylglycerols (DGDGs) (13-17%), monogalactosyldiacylglycerols (5-6%), N-acylphosphatidylethanolamines (NAPEs) (4-5%), and phosphatidylcholines (PCs) (4-6%) [3]. All such lipids were detected in the bound lipid fractions, i.e., the lipids extracted with WSB, of the investigated flours (Figure 3).…”

“…In naturally occurring lipids (of plant and animal origin), FAs are mostly esterified to glycerol or other alcohols (such as cholesterol) or linked by amide bonds to long-chain bases (sphingoids or bases thereof) or, exceptionally, to other amines. They may also contain carbohydrates, phosphoric groups and/or organic bases [2,3]. Simple lipids such as the glycerol esters of FAs are composed of only two different types of structural moieties, whereas complex lipids have more than two types of structural moieties.…”

“…Simple lipids such as the glycerol esters of FAs are composed of only two different types of structural moieties, whereas complex lipids have more than two types of structural moieties. This is, e.g., the case for phospho-and galactolipids [3,4]. Based on the presence of alkyl moieties other than FAs in their structure, lipids are subdivided in classes.…”

“…To illustrate the potential of the technique, the HPLC-ELSD method of Gerits and coworkers [33,34] was used to study the lipid profiles of different wheat flours. Wheat flour lipids, although only present in low levels (i.e., typically 2-3%), have important effects in the manufacture of wheat-based products such as bread [3,48]. To unravel the mechanisms whereby they exert these effects, it is indeed important to have appropriate techniques.…”