This document summarizes a study that evaluated the effect of adding inulin or agave fructans to reduced fat fermented lactic beverages on their composition, microstructure, rheology, and sensory properties. Scanning electron micrographs showed the protein networks of beverages containing fructans had casein micelles covered with fructan chains, while beverages with inulin contained independent inulin-gelled structures within the protein network. Rheological and sensory properties of beverages with 6% inulin, 4% inulin, or 6% fructans were comparable to the full fat control beverage. The addition of inulin or fructans improved texture and reduced syneresis compared to reduced

1. EFFECT OF INULIN AND AGAVE FRUCTANS ADDITION ON THE RHEOLOGICAL, MICROSTRUCTURAL
AND SENSORY PROPERTIES OF REDUCED FAT FERMENTED LACTIC BEVERAGES
1C. Lobato-Calleros, 1G. Crispín-Isidro, 2H. Espinosa-Andrews
1Departamento de Preparatoria Agrícola y Posgrado en Ciencia y Tecnología Agroalimentaria, Universidad Autónoma Chapingo, Km. 38.5 Carretera México –Texcoco, Texcoco, Edo. México 56230, México
2Unidad de Tecnología Alimentaria, Centro de Investigación y Asistencia en Tecnología y Diseño del Estado de Jalisco, A.C. Av. Normalistas #800, Guadalajara, Jalisco 44270, México
ABSTRACT
The composition, rheology, microstructure, and sensory acceptability of reduced-fat fermented lactic beverages (RF and RI) added with different concentrations (2, 4 or 6 % w/w) of medium chain inulin
(I) or agave fructans (F) were evaluated in comparison with those showed by a full-fat (FC) and a reduced-fat (RF) control beverages. Scanning electron micrographs showed that the casein micelles
forming the protein network of the RF beverages were covered with amorphous structures attributed to fructans chains; while the protein network of the RI beverages contained intermingled but
independent inulin gelled structures. As higher was the concentration of inulin or fructan higher was the viscoelastic response of the protein network of the RF and RI beverages. RI6, RI4, and RF6
beverages displayed rheological and sensory characteristic comparable with those of the FC beverage.
INTRODUCTION
Metabolic syndrome is a combination of three or more of the following: overweight/obesity,
hypertension, disturbances of lipid and carbohydrate metabolism, elevated triacylglyceride
concentrations, and low levels of high-density lipoproteins (HDL) in blood. It has been established that is
possible to prevent or delay metabolic syndrome through lifestyle and nutritional changes. For example,
fiber dietary intake may modulate parameters associated with the control of the metabolic syndrome
because of its prebiotic and soluble dietary fiber properties.
Fructans extracted from chicory roots (inulin-type fructans) and Agave tequilana are able to promote
the production of satietogenic/incretin peptides in the lower part of the gut, with promising effects on
glucose metabolism, body weight and fat mass development. Inulin has been used to replace fat while
improving taste and mouthfeel of dairy products.
In contrast, there are no reports in the literature dealing with the effect of agave fructans on the
physicochemical and sensory characteristics of different types of foods. The branched structure of agave
fructans may confer different functional properties than those reported for linear fructans of inulins,
giving way to new technological applications.
The objective of this study was to evaluate and contrast the effect of adding agave fructans and inulin to
reduced fat fermented lactic beverages (FLB) upon their composition, rheology, microstructure, and
sensory acceptability.
MATERIALS AND METHODS
Fermented lactic beverages variations
Full-fat control (FC; 2.6 % w/w milk fat); reduced-fat control (RC; 1.3 % w/w milk fat); and six reduced-fat
beverages (1.3 % w/w milk-fat) containing medium chain inulin (I) or Agave fructans (F) (2.0, 4.0 or
6.0 % w/w) yielding RI2, RI4, RI6, RF2, RF4, and RF6 beverages, respectively. All of the variations had 10.3
% w/w of non-fat milk solids and 2.8 % w/w of protein.
Fermented lactic beverages characterization
Chemical composition and syneresis
Rheological properties. Amplitude sweeps (0.01–100 % strain, 1 Hz) and frequency sweeps (0.01-100 Hz,
0.2 % strain). (Physica MCR 301 Shear Rheometer, Anton Paar, Messtechnik, Stuttgart, Germany). G’ and
G” values were obtained from the equipment software
Microstructure (Scanning Electron Microscopy)
Sensory attributes (acidity, flavor, creaminess, sweetness, granularity, viscosity) and overall acceptability
using a nine-point hedonic scale (1 = dislike extremely, 2 = dislike very much, 3 = dislike moderately, 4 =
dislike very little, 5 = neither like nor dislike, 6 = like a little, 7 = like moderately, 8 = like very much, and 9
= like extremely)
RESULTS AND DISCUSSION
Chemical composition and syneresis of the fermented lactic berverages
The FC beverage had a fat content that was higher (p ≤ 0.05) than that of the RC, RF and RI beverages
(Table 1). All of the FLB variations showed similar (p > 0.05) protein content, as this was standardized at
2.8 % w/w. Increasing F and I levels increased total solids values of the FLB. In general, the RF and RI
beverages exhibited lower values of syneresis than those exhibited by FC and RC beverages (Table 1).
Table 1. Chemical composition and syneresis of the fermented lactic beverages
FLB code Fat
(%)
Protein
(%)
Total solids
(%)
Acidity
(°D)
Syneresis
(%)
FC 2.7 ± 0.1b 2.9 ± 0.1a 17.4 ± 0.2ab 78.5 ± 0.7a 9.9 ± 0.6c
RC 1.3± 0.0a 2.7± 0.1a 16.9 ± 0.3a 83.0 ± 1.4ab 13.5 ± 1.5d
RF2 1.3± 0.0a 2.9 ± 0.3a 18.3 ± 0.4b 85.0 ± 1.4b 5.0 ± 0.4ab
RF4 1.3± 0.0a 2.8 ± 0.1a 22.1 ± 0.1de 86.0 ± 1.4b 3.7 ± 0.3ab
RF6 1.3± 0.0a 3.0 ± 0.3a 22.6 ± 0.6e 85.5 ± 2.1b 2.6 ± 0.2a
RI2 1.3± 0.0a 2.9 ± 0.0a 20.1 ± 0.1c 86.0 ± 1.4b 9.2 ± 0.9c
RI4 1.3± 0.1a 2.9 ± 0.0a 20.9 ± 0.4cd 84.0 ± 1.4ab 5.3 ± 0.5b
RI6 1.3 ± 0.0a 3.0 ± 0.0a 22.5 ± 0.4e 86.5 ± 0.7b 5.1 ± 0.1ab
FC: full-fat beverage control; RC: reduced-fat beverage control; RF and RI: reduced-fat beverages containing agave
fructans or inulin (2, 4 or 6 % w/w), respectively.
a,b,c,d,e: different superscripts within the same column indicate that the means differ significantly (p ≤ 0.05).
Microstructure of the fermented lactic beverages
The microstructure of FC and RC beverages can be observed from the SEM micrographs (Fig. 1). FC
microstructure (Fig. 1a) was mainly composed by aggregates and chains of casein forming three-dimensional
networks, in which originally fat droplets, whey and lactic bacteria were trapped. The
protein network of RC (Fig. 1b) was less dense, more open, and with more void spaces than that of the FC
as consequence of smaller fused casein micelles aggregates, probably due to lower number of fat
globules acting as linking protein agents.
a b
The microstructure of the RF and RI beverages was formed by protein networks with differing
structures between them and respect to those of the FC and RC beverages (Figs. 2 and 3). The RF
beverages microstructure (Fig. 2) was composed by chains of fused casein micelles covered by an
amorphous material attributed to fructans chains. As higher was the F concentrations more
uniformly were covered the micelle caseins and more compact was the resulting protein network.
a b c
Fig. 2. Scanning electron micrographs of the reduced-fat lactic beverages containing Agave fructans (F): (a) RF2 (with 2
% w/w of F); (b) RF4 (with 4 % w/w of F); and RF6 (with 6 % w/w of F). Magnification is 10 000×, scale bar=1 m.
The RI beverages microstructure (Fig. 3) was characterized by the presence of apparently inulin
gelled structures, intermingled but forming independent structures to the protein network. As
higher was the I concentration more numerous gelled particles were observed into the protein
network. It has been informed that the capability of inulin for gel formation and the subsequent gel
strength is dependent of its polymerization degree; as higher is the long chain greater propensity of
inulin to form gelled structures; in contrast, small chains remains soluble.
a b c
Fig. 3. Scanning electron micrographs of the reduced-fat lactic beverages containing medium chain inulin (I): (a) RI2
(with 2 % w/w of I); (b) RI4 (with 4 % w/w of I); and RI6 (with 6 % w/w of I). Magnification is 10 000×, scale bar=1 m.
Rheological properties of the fermented lactic beverages
The variations of G′ and G′′ with frequency for the FLB are shown in Fig. 4. Independently of their
composition, the FLB exhibited a storage modulus characterized by showing a slightly increase in
gradient with frequency. In all cases the G′ and G′′ values corresponded to a weak gel structural
network, where G′ was always greater than G′′ in the range of frequencies studied. Although, the
development of G′ and G′′ with frequency was qualitatively similar for the eight variations of FLB,
differences between the G’ and G’’ values at a same frequency were observed. Thus, at 1 Hz of
frequency the G’ values of the FC (69.8 Pa) beverage was no significantly different from those of RI6
(84.9 Pa), RI4 (63.2 Pa), and RF6 (55.25 Pa). The G’’ values for these FLB followed a similar trend.
100
10
1
0.01 0.1 1 10 100
G' [Pa]
Frequency [Hz]
FC
RC
RF
2
RF
4
RF
6
RI
2
RI
4
RI
6
100
10
1
0.01 0.1 1 10 100
G'' [Pa]
Frequency [Hz]
CF
RC
RF
2
RF
4
RF
6
RI
2
RI
4
RI
6
Fig. 4. Variation of the storage modulus (G’) and loss modulus (G’’) of the fermented lactic beverages
as a function of frequency.
Sensory evaluation of the fermented lactic beverages
The great majority of the sensory attributes (acidity, creaminess, sweetness, granularity, and viscosity) of
the reduced-fat FLB were perceived as similar (p > 0.05) from those showed by the FC beverage (Table 2).
In contrast, the flavor and overall acceptability of the RF4 received a higher acceptability scores than
those of the FC beverage.
Table 2. Sensory acceptability scores of the fermented lactic beverages
FLB
code
Acidity Creaminess Sweetness Granularity Flavor Viscosity Overall
acceptability
CF 7.0 ± 1.7ab 7.6 ± 1.3abc 7.1 ± 1.9ab 7.5 ± 1.5ab 7.2 ± 2.0ab 7.7 ± 1.1ab 7.5 ± 1.8ab
RC 7.3 ± 1.7ab 7.5 ± 1.5abc 6.9 ± 1.8a 7.5 ± 1.4ab 7.3 ± 1.7ab 7.4 ± 1.4ab 7.4 ± 1.7ab
RF2 6.7 ± 1.8a 7.1 ± 1.6ab 6.6 ± 1.8a 7.7 ± 1.4ab 6.7 ± 1.8a 7.0 ± 1.7a 6.9 ± 2.0a
RF4 7.9 ± 1.6 b 7.3 ± 1.4b 8.0 ± 1.6 b 8.2 ± 1.6b 8.4 ± 1.3c 8.0 ± 1.4b 8.5 ± 1.6 c
RF6 7.4 ± 1.3ab 7.3 ± 1.3ab 7.5 ± 1.5ab 7.5 ± 1.3ab 7.6 ± 1.7abc 7.1 ± 1.3a 7.8 ± 1.5bc
RI2 7.5 ± 1.5ab 7.7 ± 1.4bc 8.0 ± 1.3b 7.6 ± 1.3ab 8.1 ± 1.3bc 7.7 ± 1.3ab 8.0 ± 1.3bc
RI4 7.1 ± 1.7ab 6.9 ± 1.6a 7.0 ± 1.9ab 7.3 ± 1.5a 6.9 ± 1.9a 6.9 ± 1.8a 6.6 ± 1.7a
RI6 7.1 ± 1.8ab 7.6 ± 1.2abc 7.3 ± 2.0ab 7.0 ± 1.8a 7.3 ± 2.0ab 7.3 ± 1.4ab 7.3 ± 1.7ab
FC: full-fat beverage control; RC: reduced-fat beverage control; RF and RI: reduced-fat beverages containing agave
fructans or inulin (2, 4 or 6 % w/w), respectively.
a,b,c: different superscripts within the same column indicate that the means differ significantly (p ≤ 0.05).
CONCLUSIONES
In this work, it was established that reduced-fat fermented lactic beverages manufactured from
reconstituted partially skim milk and Agave fructans (6 % w/w) or medium chain inulin (4 and 6 % w/w)
emulated the rheological and sensory characteristics of its full-fat counterpart, despite their completely
different structural arrangements. Fructans chains were completely integrated unto the protein network
increasing its strength and strain resistance; while inulin chains formed secondary gelled structures that
contributed to the mechanical behavior of the protein network. Additionally, syneresis propensity of the
reduced-fat fermented lactic beverages containing inulin or Agave fructans was in general lower than
that of the full-fat fermented lactic beverage.
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Fig. 1. Scanning electron micrographs of the FLB beverages control: (a) full-fat (FC) and (b)
reduced-fat (RC). Magnification is 10 000×, scale bar=1 m.