Progressive Pearling of Barley Kernel: Chemical Characterization of

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Progressive pearling of barley kernel: new ingredients for the production of functional breads Massimo Blandino, Monica Locatelli, Valentina Sovrani, Jean Daniel Coisson, Luca Rolle, Fabiano Travaglia, Simone Giacosa, Matteo Bordiga, Valentina Scarpino, Amedeo Reyneri, and Marco Arlorio J. Agric. Food Chem., Just Accepted Manuscript • DOI: 10.1021/jf506193p • Publication Date (Web): 30 Mar 2015 Downloaded from http://pubs.acs.org on April 14, 2015

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Journal of Agricultural and Food Chemistry

Progressive pearling of barley kernel: chemical characterization of pearling fractions and effect of their inclusion on the nutritional and technological properties of wheat bread.

Authors: Massimo Blandinoa, Monica Locatellib, Valentina Sovrania, Jean Daniel Coïssonb, Luca Rollea, Fabiano Travagliab, Simone Giacosaa, Matteo Bordigab, Valentina Scarpinoa, Amedeo Reyneria, Marco Arloriob*.

Affiliation: a

University of Turin, Dipartimento di Scienze Agrarie, Forestali e Alimentari, Largo Paolo

Braccini 2, 10095 Grugliasco (TO), Italy. b

University of Piemonte Orientale, Dipartimento di Scienze del Farmaco, Largo Donegani 2,

28100, Novara (NO), Italy.

* Corresponding author: Tel: +39-0321-375772; fax +39-0321-375751. E-mail address: [email protected]

1

ACS Paragon Plus Environment


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Abstract

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Two hulled varieties have been sequentially pearled for 1 to 8 cycles, each with 5% removal. The

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derived fractions were analyzed for their bioactive compound content. The dietary fiber (DF)

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decreased from the external to the internal layers, while β-glucans showed an inverse trend.

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Deoxynivalenol contamination was concentrated in the outer layers. The total antioxidant activity

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(TAA) was higher in the 15-25% fractions, which were used to prepare bread. Five mixtures of

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refined wheat flour, with an increasing replacement of this pearled barley fraction, were compared

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with a control for the bioactive compound content, as well as for the rheological and physical bread

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properties. The inclusion of pearled fractions with up to a 10% substitution leads to a clear

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enhancement of the DF and TAA, with only minor detrimental effects on the physical parameters.

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Selected by-products of barley pearling could be proposed as functional ingredients for bakery

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products rich in DF and TAA.

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Keywords: barley, pearling, antioxidant activity, bioactive compounds, dietary fibre, β-glucan,

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phenolic compounds, bakery products.

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Introduction

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Today there is an increasing demand for functional food, that is, products fortified with special

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constituents that possess advantageous physiological effects (1). Cereals offer multiple beneficial

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effects related to the contents of several non-digestible carbohydrates and antioxidant compounds

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(2), and allow novel cereal foods or ingredients that can target specific populations to be designed.

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Moreover, bakery products, including bread, provide an ideal matrix by which functionality can be

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delivered to the consumer in acceptable food.

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The majority of consumed cereal food is prepared with refined flour, mainly due to texture and taste

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perception reasons, but in this form they contain less health-promoting compounds that are instead

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present in the whole grain raw material. Thus, in developing functional bakery products, it is

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necessary to realize a food which can deliver the appropriate level of bioactive compounds, but

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which also meets the consumers ‘ requirements in terms of appearance, taste and texture (3).

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Among cereals, barley (Hordeum vulgare L.) is gaining growing importance as a functional

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ingredient, due to its high nutritional significance (4). Barley grain provides high levels of dietary

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fiber (DF), with general and specific health benefits. Moreover, barley is particularly rich in an

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important soluble DF component, a non-starch unbranched polysaccharide composed of (1→4) and

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(1→3) linked β-D-glucopyranosyl units, simply known as β-glucan (5,6). Health claims for barley

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have been approved by the Food and Drug Administration (7) and EFSA (8).

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The protective effects of cereal fibers depend on their solubility: soluble fibers, particularly β-

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glucans, can reduce blood cholesterol and regulate blood glucose levels for diabetes management,

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while insoluble fibers shorten the transit time through the intestinal tract, thus reducing the risk of

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colorectal cancer, and can positively affect weight control, through their satiety effect (9). In

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addition to the DF content, barley is an important source of other bioactive compounds, and some of

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them, in particular phenolics, such as phenolic acids, lignans and flavonoids, show a marked

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antioxidant activity (10,11).

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Although much is known about the nutritional and health benefits of barley consumption, much less

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has been reported about the use of its grain components, in terms of processing and food product

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development. The principal uses of this cereal are as livestock feeds and, to a lesser extent, as grain

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for malting and brewing. The traditional food processing of barley produces pot and pearled barley,

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flakes and flour by roller-milling pearled barley. The inedible hull is firmly attached to the pericarp,

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thus barley grains are generally pearled through an abrasive scouring process that gradually

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removes the hull, bran, with the seed coat (testa and pericarp) and aleurone layers, and the germ.

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Pearled barley usually represents ≈60-70% of the total grain weight, but may be adjusted,

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depending on the purpose of the final product (12). The by-products of the pearling process (≈30-

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40% w/w) are mainly used in animal feeds, although the abraded material is a potential natural

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source of phytochemicals (13). The main challenge of adding these by-products to bakery products

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is to find new processing strategies in order to incorporate more of the bioactive compounds in

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flour, while still removing those parts of grain which confer inferior technological quality or affect

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safety (3). In general, DF additions to baking lead to important reductions in the loaf volume, and a

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different texture of the breads is obtained, thus the optimal proportion of DF addition to each

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different food should also be determined on the basis of sensory attributes.

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The cereal grain fractionation technology, which could also be applied easily with a selective dry

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pearling process, is receiving a great deal of attention because of its capacity to efficiently

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separate negative and positive aspects, in order to produce new ingredients and flour mixes with

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technologically optimized functional and nutritional attributes (14,15). The sequential pearling of

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wheat kernel and the incorporation of selected pearled fractions into the bread formula was studied

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in previous works (16, 17).

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The effects of the inclusion of barley wholegrain or bran fractions were previously reported by

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several authors, who focused separately on the nutritional benefits (18-22) or the technological 4


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consequences (23-26). However, the addition of intermediate barley pearled fractions to bread-

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making has not yet been considered.

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The aims of this study were: i) to analyse the bioactive compound contents and detrimental factors

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in barley kernels, through a sequential pearling process, in order to use them as functional food

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ingredients; ii) to comprehensively evaluate the nutritional enhancement and the technological

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impact of the incorporation, at different replacement levels, of an intermediate pearled barley

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fraction into bread formulations.

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Materials and methods

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Field barley production

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Two commercial winter barley varieties were cultivated side by side in the same field, in a

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medium-texture fertile soil in Carignano, NW Italy (44°53'8.69"N, 7°41'16.75"E, 232 m a.s.l.),

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during the 2011-12 growing season, according to the normal crop management program applied in

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the growing area.

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The compared barley varieties were: Trasimeno (Geo Seed, Grinzano di Cervere, CN, Italy) a two-

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row cultivar and Ketos (Limagrain Italia Spa, Busseto, PR, Italy) a six-row cultivar. Both cultivars

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have hulled grains.

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Planting was conducted in 12 cm wide rows at a seeding rate of 450 seeds m-2 on October 24, 2011.

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The previous crop was maize for grain and the seed bed was set after ploughing (30 cm) and

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harrowing. A total of 130 kg N ha-1 was applied as a granular ammonium nitrate fertilizer, split

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equally between the tillering and stem elongation stages. Harvest was conducted with a combine-

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harvester in June 23, 2012. Kernel samples of each cultivar were stored at 4°C until the beginning

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of the pearling tests.

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Sequential grain pearling

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Nine fractions of kernels from each cultivar were obtained through incremental pearling, following

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the approach proposed by Beta et al. (27). The pearling consisted of consecutive passages of barley

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whole grain and pearled grain in an abrasive-type grain testing mill (TM-05C model, Satake,

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Tokyo, Japan) at a constant speed of 1100 rpm and frequency of 55 Hz. The pearling process was

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monitored by time control. After each assay, the laboratory pearler was cleaned thoroughly by

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means of dust aspiration and compressed air, to minimize equipment contamination. Initially, a 500

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g portion of each unprocessed barley was sub-sampled from a 5 kg sample, and the remaining 4.5

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kg was pearled. Starting from with unprocessed grain, kernels were initially pearled to remove 5%

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of the original grain weight, and this resulted in a first fraction (0-5% w/w). The remaining kernels

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were then pearled to remove a second fraction of 5% (5-10% w/w). The pearling process was

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continued until another 6 fractions (designed 10-15%, 15-20%, 20-25%, 25-30%, 30-35% and 35-

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40%, respectively) plus a residual 60% of the kernel (40-100%) had been collected.

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The whole grain samples and the residual 60% of the unprocessed kernels were milled using a

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laboratory centrifugal mill (ZM-100; Retsch, Haan, Germany) with a 1 mm opening. Then, both the

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milled and pearled samples (500 g) were ground to pass through a 0.5 mm sieve and stored at -25°C

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until the chemical analyses.

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Substitution of flour with barley pearled fraction in the bread making procedure

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A functional ingredient was obtained from the barley pearling, following the approach proposed in

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a previous study focused on wheat (17). The two-row Trasimeno barley, which showed the lower

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DON content and the higher β-glucan content, was chosen to prepare an intermediate pearled

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fraction, in order to obtain a functional ingredient that would preserve a high functional role, but

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without those parts of grain that could confer inferior technological quality or affect safety. 6


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Considering that the fiber, proteins, minerals and antioxidant compounds are concentrated in the

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most external layers, but β-glucans are presents in a greater concentration in the inner part of the

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barley kernel, the best compromise to preserve all these functional compounds appeared to be the

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15-25% (w/w) fraction. In fact, the total and insoluble DF in the selected pearled fraction was still

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high, and although the more external coarse fiber, located in the hull, and the more external

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endosperm layers were removed, a good β-glucan content was still provided.

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Starting from unprocessed grain, the barley kernels were initially pearled to remove 15% of the

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original grain weight, according to the previously reported procedure, and this most external

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fraction was discarded. The remaining kernels were then pearled to remove a second 10% fraction

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of the original grain weight (15-25%), and this fraction was used to replace refined commercial

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bread-making flour at different percentages.

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Five mixtures of refined commercial bread-making flour, with an increasing replacement rate (5%,

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10%, 15%, 20%, 25%) of the selected pearled barley fraction, were obtained and employed for

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bread making. Refined flour and the selected pearled barley fraction were accurately mixed using a

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rotary laboratory blender (Beccaria S.r.l., Cuneo, Italy). The Chopin® alveograph parameters of the

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commercial refined flour were: deformation energy (W) 325 J 10-4 and curve configuration ratio

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(P/L) 0.52. The particle size of the selected pearling fraction was similar to that of the refined

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commercial flour: in both cases, more than 80% of the particles were < 200 µm.

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The breads were made according to the AACCI Method 10-10.03 for 3 kg of flour (28). The

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formula contained salt (2% of flour weight), brewer yeast (3% of flour weight) and the optimal

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water absorption, which was previously determined through a Mixolab® rheological analysis. The

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dough was then mixed in a spiral mixer (Esmach®, Bonpard Group, Vicenza, Italy) and divided into

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three pieces of approximately 400 g/piece, to obtain three loaves, which were placed in baking tins

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(10.5 x 6 cm2 and 6.5 cm deep). The mixing times were different for the refined commercial and the

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selected pearled barley fraction mixtures, in order to obtain an equivalent dough development. After 7



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fermentation (at 30°C and a relative humidity of 85% for 120 min), the loaves were baked at 215°C

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for 45 min.

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The three composite loaves for each replacement level were used as replicates for chemical and

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technological analyses.

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Chemicals

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The total Dietary Fiber (DF) and Mixed-Linkage β-Glucan kits for enzymatic determinations were

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supplied by Megazyme (Megazyme International Ireland Ltd, Wicklow, Ireland). The solvents

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(HPLC or GC grade) and formic acid (50%, LC–MS grade) were purchased from Sigma–Aldrich

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(Milan, Italy). The water was obtained from Milli-Q instrument (Millipore Corp., Bedford, MA,

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The USA). The antibody-based immunoaffinity columns were supplied by VICAM (Waters

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Corporation, Watertown, MA, The USA). The analytical standards (purity ≥ 95%) and all the other

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chemicals (reagent-grade level) were purchased from Sigma–Aldrich (Milan, Italy).

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Chemical analyses on pearling fractions and breads

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Sample preparation

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Bread samples were ground in a laboratory mill (ZM-100; Retsch, Haan, Germany), and in the case

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of DF, the total phenolic content (TPC) and the total antioxidant activity (TAA) determinations,

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they were further freeze-dried (Heto Drywinner 8, Copenhagen, Denmark) and ground in an

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oscillatory mill (Mixer Mill MM440, Retsch GmbH, Hann, Germany). The barley pearled fractions,

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the whole flours and the freeze-dried ground breads were sieved (particles size

Progressive Pearling of Barley Kernel: Chemical Characterization of

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