**Application of Dairy Proteins as Technological and Nutritional Improvers of Calcium-Supplemented Gluten-Free Bread**

**Urszula Krupa-Kozak 1,- 1,2 and Cristina M. Rosell 2** 


*Received: 29 August 2013; in revised form: 29 October 2013 / Accepted: 4 November 2013 / Published: 14 November 2013* 

**Abstract:** Effect of dairy proteins on gluten-free dough behavior, and nutritional and technological properties of gluten-free bread was evaluated. Experimental doughs, containing dairy powders, showed low consistency. Obtained gluten-free breads were rich in proteins, and, regarding the energy value delivered by proteins, they could be considered as a source of proteins or high in proteins. Applied dairy proteins affected the technological properties of experimental breads causing a significant (*p* < 0.05) increase of the specific volume, crust darkening, and crumb lightness, depending on the dairy supplementation level, rather than the protein type. Dairy proteins incorporated at a 12% level, significantly (*p* < 0.05) decreased the hardness; nevertheless, the highest amount of proteins tested led to the opposite effect. These results indicate that milk proteins tested could be successfully added to gluten-free bread with beneficial effects on technological and nutritional properties.

**Keywords:** dairy proteins; gluten-free bread; dough consistency; technological properties; nutritional value; celiac disease

#### **1. Introduction**

Celiac disease (CD) is a chronic immune-mediated intestinal disorder that develops in individuals having genetic predispositions with multiple contributing genes. The most important are HLA-DQ2 and HLA-DQ8, however, non-HLA genes also contribute to the development of CD. Approximately 1% of the worldwide population is suffering from CD, and, thus, this disorder is classified as one of the most common food intolerances [1,2]. CD is related to permanent intolerance to gluten, a storage protein found in wheat (gliadin), rye (secalins), barley (hordeins), and, probably, in some oat (avenins) cultivars. A great deal is known on the sequential pathophysiological events driving the intestinal inflammatory cascade [3–5] The immune response in CD involves the adaptive, as well as the innate, and is characterized by the presence of anti-gluten and anti-transglutaminase 2 antibodies, lymphocytic infiltration in the epithelial membrane and the lamina propria, and expression of multiple cytokines and other signaling proteins. The disease leads to inflammation, villous atrophy, and crypt hyperplasia in the small intestine. Mentioned factors can contribute to malabsorption of several nutrients (iron, folic acid, calcium, and fat-soluble vitamins) [6], general malnutrition, and reduced body mass index (BMI) [7]. Currently, strict and life-long adherence to a gluten-free diet (GFD) remains the only effective treatment for CD.

Generally, gluten-free formulas and baked products are poor in proteins [8]. In traditional baking industry proteins derived from plants (proteins of soya) and animal origin (milk proteins and egg albumins) are frequently used [9,10]. Milk proteins are highly functional ingredients characterized by a significant nutritional value. They swell in a high level and are able to build up a network [11,12]. Next to the functional benefits, gluten-free products with milk proteins are affluent in calcium and proteins, and, thus, enriched in essential amino acids like lysine, methionine and tryptophan [13]. Milk proteins can be successfully added to gluten-free products with beneficial effects on the technological properties. Caseinates are good emulsifiers and stabilize the batter; isolated and concentrated whey proteins can form gels; high temperature skim milk powder exhibits high water-binding capacity [10]. Whey proteins increased the specific volume and decreased bread crumb hardness over time, while sodium caseinate demonstrated the opposite effect [14]. On the contrary, the addition of both - whey proteins concentrate and sodium caseinate to short biscuit formulation, raised hardness and intensified surface brownness [15]. To improve the nutritional value of gluten-free products by the addition of milk proteins particular attention should be paid to the lactose content [16]. Celiac patients are often susceptible to secondary lactose intolerance due to alterations of lactase secretion resulted from the villous atrophy [6]. The addition of high protein/low lactose dairy powders combined with optimal amount of water resulted in gluten-free breads rich in proteins, with dark crust and white crumb, good acceptability scores in sensory tests, an increase in loaf volume, and a decrease in crust and crumb hardness [17].

There is a justified need to improve the nutritional value of gluten-free products. The present study is a continuation of previous trials on the enhancement of the quality and nutritional value of gluten-free bread [18], this time focused on the fortification in proteins. The aim of the study was to enrich a gluten-free formulation, supplemented with calcium citrate in low-lactose dairy proteins, to evaluate its mixing and pasting behavior and to analyze the technological properties, overall quality, and sensory characteristics of obtained gluten-free bread.

#### **2. Experimental Section**

#### *2.1. Materials*

Corn starch (Huici Leidan SA, Huarte, Spain), potato starch (EPSA, Valencia, Spain), pectin (E 440(i` ª«£¬ « ^ 
 ® « ` 
 
 ~
« ` 
 
{AS; POCh, Gliwice, Poland), spray dried whey protein isolate (ISO; Carbery Ballineen, Ireland), and hydrolyzed whey proteins (OPT; Carbery Ballineen, Ireland). The amount of protein components was determined on the basis of nutrition and health claims made on foods in such a way that the final gluten-free product was either a source of protein or high in protein [19].

#### *2.2. Characteristic of Dairy Powders*

#### 2.2.1. Chemical Composition of Dairy Ingredients

The moisture, crude proteins (N × 6.25), and ash contents were evaluated using the standard methods [20–22]. The results presented are the mean values of at least two replicates.

#### 2.2.2. Physical and Functional Properties of Dairy Ingredients

Particle size distribution was determined using a Mastersizer 2000 Particle Size Analyzer with a wet dispersion unit Hydro 2000 S (Malvern Instrument Ltd, Malvern, England). Samples (1–2 g) were suspended in isopropanol. In order to keep the sample suspended and homogenized, it was recirculated continuously through the measurement zone. Particle size distribution was assessed using the mean particle volume (D50) in six replicates for each sample.

The measurement of color was performed by using a Minolta colorimeter (Chroma Meter CR-400/410, Konica Minolta, Japan), equipped with a granular attachment after standardization with a white calibration plate. The color was expressed in accordance with CIE-*L\*a\*b\** uniform color space (CIE-Lab). The parameters determined were lightness *L*\* (*L*\* = 0 [black] and *L*\* = 100 [white]), *a*\* (*a*\* = greenness and +*a*\* = redness), and *b*\* (*b*\* = blueness and +*b*\* = yellowness). Values were the mean of nine replicates.

Water absorption index (WAI) and water solubility index (WSI) were determined according the method of Anderson *et al*. [23] at room temperature (RT) and after heating. Oil absorption capacity (OAC) was determined according to the method of Lin, Humbert, and Sosulski [24]. The values presented are the average of three measurements.
