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https://dx.doi.org/10.1016/j.lwt.2014.10.045
http://hdl.handle.net/10251/64802
Elsevier
Bernat Pérez, N.; Cháfer Nácher, MT.; Rodriguez Garcia, J.; Chiralt A.; González Martínez,
MC. (2015). Effect of high pressure homogenization and heat treatment on physical
properties and stability of almond and hazelnut milks. Food Science and Technology.
62:488-496. doi:10.1016/j.lwt.2014.10.045.
Effect of high pressure homogenisation and heat treatment on physical 1
properties and stability of almond and hazelnut milks 2
3
Bernat N
1
, Chafer M
1
, Rodríguez-García, J
2
, Chiralt A
1
and Gonzalez-Martínez, C
1*
. 4
(1) Institute of Food Engineering for the Development. 5
(2) Food Technology Department. 6
Universitat Politècnica de Valencia, Camino de Vera s/n, 46022 Valencia, Spain. 7
(cgonza@tal.upv.es) 8
9
ABSTRACT 10
11
The effect of high pressure homogenisation (HPH) and heat treatments on physicochemical 12
properties and physical stability of almond and hazelnut milks was studied. Vegetable milks were 13
obtained and homogenised by applying 62, 103 and 172 MPa (MF1, MF2 and MF3, respectively). 14
Untreated and MF3 samples were also submitted to two different heat treatments (85ºC/30 min 15
(LH) or 121ºC/15 min (HH)). Physical and structural properties of the products were greatly 16
affected by heat treatments and HPH. In almond milk, homogenised samples showed a significant 17
reduction in particle size, which turned from bimodal and polydisperse to monodisperse 18
distributions. Particle surface charge, clarity and Whiteness Index were increased and physical 19
stability of samples was improved, without affecting either viscosity or protein stability. Hazelnut 20
beverages showed similar trends, but HPH notably increased their viscosity while change their 21
rheological behaviour, which suggested changes in protein conformation. HH treatments caused 22
an increment of particle size due to the formation oil droplet-protein body clusters, associated 23
with protein denaturation. Samples submitted to the combined treatment MF3 and LH showed the 24
greatest stability. 25
26
Key words: Particle size, DSC, viscosity, ζ-potential, confocal. 27
1
Abbreviations: 28
CLSM, confocal laser scanning microscopy; DSC, differential scanning calorimetry ; HH, high 29
heat; HPH, high pressure homogenisation; PI, isoelectric point; LH, low heat; MF1, 30
homogenisation at 62 MPa; MF2, homogenisation at 103 MPa; MF3, homogenisation at 172 31
MPa; WI, whiteness index. 32
33
1. INTRODUCTION 34
35
In the last few years, the population ratio demanding vegetable-based products is growing, either 36
because of the increasing problems related with the intolerances to Cow’s milk (Fiocchi et al., 37
2010) or because of changes in the food preferences. As a consequence of new consumer 38
tendencies, food industries are currently producing new nutritionally improved products with 39
added value. Vegetable-based beverages are included in these new products, which are available 40
at any supermarket as an alternative to dairy products, with an increasing consumer acceptance. 41
There is a wide variety of vegetable-based beverages, although most of the research activity has 42
been focused on those obtained from soy. For soy “milk”, studies into the physicochemical 43
characterization, the effects of processing, the application of new technologies, such as electric 44
pulses and ultra-high homogenisation pressures have been carried out (
Cruz, Capellas, Hernández, 45
Trujillo, Guamis, & Ferragut, 2007; Li, Chen, Liu, & Chen, 2008). 46
Research dealing with the use of non-soy vegetable milk is still scarce and most of it is related 47
with the nutritional quality of such products. In this sense, almond and hazelnut beverages have 48
been used as an alternative to milk in lacto-intolerant people, pregnant women and celiacs, due to 49
their high levels of calcium, phosphorous and potassium (Eroski Foundation, 2007; Luengo, 50
2009). These nuts have low sodium content and an equilibrated mono-unsaturated fatty acid-51
polyunsaturated fatty acids ratio, which define the products which are healthy for people with 52
heart disease (Mateos, 2007). They are also considered helpful for maintaining cholesterol at 53
healthy levels due to their high content of antioxidant compounds which contributes to heart 54
disease prevention (Fraser, Bennett, Jaceldo & Sabaté, 2002; Jenkins, Kendell, Marchie, Josse, 55
2
Nguyen & Faulkner, 2008; Kris-Etherton, Hu, Rose & Sabaté, 2008; Tey, Brown, Chislholm, 56
Delahunty, Gray & Williams, 2011). 57
Vegetable based beverages are emulsified products where the nut fat is dispersed in an aqueous 58
phase and where the rest of the components play different roles in the product stability. The 59
different process steps, such as homogenisation and heat treatments usually produce changes in 60
the arrangement of components, thus leading to modifications in the particle size, colour, viscosity 61
and physical stability of the product. These physicochemical modifications have to be known to 62
efficiently control the process and to implement the necessary improvements in the production 63
lines. The most commonly used homogenisation pressures in the food industry range between 20 64
and 50 MPa, although much higher pressures are used in high pressure homogenisation (HPH) 65
processes with some advantages: the deflocculation of clusters of primary fat globules (Floury, 66
Desrumaux, & Lardières, 2000) and uniform dispersion of agglomerates, the changes in protein 67
conformation (Pereda, Ferragut, Quevedo, Guamis & Trujillo, 2009), the increase in emulsion 68
viscosity (Desrumaux & Marcand, 2002) and stability and the microbial inactivation (Diels, 69
Callewaert, Wuytack, Masschalk & Michiels, 2005; Pereda, Ferragut, Guamis & Trujillo, 2006; 70
Smiddy, Martin, Huppertz & Kelly, 2013; Cruz, Capellas, Hernández, Trujillo, Guamis & 71
Ferragut, 2007). 72
The objective of the present study is to analyze the effect of heat treatments and high 73
homogenisation pressures on the physical properties and stability of almond and hazelnut 74
beverages (nut milks) in order to define processing conditions which ensure the product quality 75
and stability. 76
77
2. MATERIALS & METHODS 78
79
2.1 Preparation of almond and hazelnut milks 80
Nut beverages were produced by soaking and grinding Prunus amygdalus L.dulcis almonds and 81
Corylus avellana hazelnuts, supplied by Frutos Secos 3G S.L. (Valencia, Spain). The extraction 82
was carried out in Sojamatic 1.5 (Sojamatic
®
; Barcelona, Spain), equipment specifically designed 83
3
for the production of vegetable beverages, with a nut-water ratio of 8:100. This equipment carries 84
out both the nut grinding and the solid particles’ retention throughout filtration. The 85
manufacturing process takes 30 minutes at room temperature, in which both grinding and filtering 86
are performed discontinuously every two minutes. The milky liquid obtained was used as control 87
sample (untreated). 88
89
2.2 High pressure homogenisation and heat treatments 90
High pressure homogenisation (HPH) treatments were carried out in a high pressure homogeniser 91
M-110P model (Microfluidics International Corporation, Newton, MA, USA) by applying 62, 92
103 and 172 MPa (samples MF1, MF2 and MF3 respectively). Some samples were submitted to 93
a low temperature heat treatment (LH) at 85 ºC for 30 min by using a temperature-controlled 94
water bath (Precisdig, JP-Selecta; Barcelona, Spain) and to a high temperature heat treatment 95
(HH), 121 ºC for 15 min in an autoclave (Precisdig, JP-Selecta; Barcelona, Spain). The heat 96
treatment conditions chosen were those in which the destruction of all vegetative cells and 97
enzymes are ensured (Walstra, Wouters & Geurts, 2006). Samples submitted to heat treatment 98
were the control samples (LH and HH samples) and those homogenised at 172 MPa (MF3LH and 99
MF3HH samples). 100
101
2.3 Characterization of chemical composition. 102
The quantification of moisture, ash, fat content, proteins and sugars was carried out in the nut 103
milks. Fibre content was estimated by means of the difference in terms of component percentages. 104
Almond beverages were freeze-dried (ioalfa-6 freeze-dryer; TELSTAR, Terrassa, Spain) prior to 105
the analysis. AOAC Official Methods were chosen to determine water, total fats and total nitrogen 106
contents (AOAC 16.006, AOAC 945.16 and AOAC 958.48, respectively) (Horwitz, 2000). Total 107
sugars and ashes were obtained following the protocols suggested by Matissek, Schnepel & 108
Steiner (1998). All the determinations were performed in triplicate. 109
110
2.4 Characterization of physical and structural properties 111
4
