Optimization of crude inulin extraction from garlic ( Allium sativum L.) 1 agro-industrial waste using the response surface methodology. 2

Inulin is a polysaccharide with several applications within the chemical, pharmaceutical, 19 and food industry. It is considered a dietary fibre that provides multiple health benefits. 20 In this work, the yield of raw inulin obtained from garlic agro-industrial useless waste was maximized, by applying the response surface methodology in a central composite 22 design (CCD), in which different distilled-water (DW)-to-garlic-agro-industrial-waste 23 (GAIW) ratios (3 and 5 mL/g) and different temperatures (60 and 80 °C) were 24 evaluated. Optimal condition was obtained with a DW/GAIW ratio of 4.3 mL/g and a 25 temperature of 80.2 °C. Under this condition, the quadratic model showed a maximum 26 yield of crude inulin of 8.17 ± 0.89 g/100 g. Further, the CCD model obtained was 27 validated with three additional experiments at the same optimal condition. The FTIR 28 spectra of inulin obtained from garlic agro-industrial residues and chicory inulin showed 29 similarities and differences, presumably related to the different degrees of 30 polymerization of the fructans present.


34
Garlic (Allium sativum L.) is an aromatic crop native to Central Asia, although its 35 cultivation has spread throughout the five continents, and has been widely used as a 36 condiment for the preparation of numerous dishes in different countries (Charron et al.   Inulin is a non-digestible fructan-type polysaccharide found in many plants as a 66 storage carbohydrate, usually in vegetables, fruits, and cereals of important nutritional 67 properties (Franck 2002(Franck , 2016Apolinário et al. 2014;Shalini et al. 2017). Inulin can be 68 used as an industrial food ingredient improving organoleptic characteristics, the stability 69 4 of foams and emulsions, and as a fat substitute offering an advantage in taste and 70 texture (Panesar and Bali 2016;Shoaib et al. 2016;James et al. 2017;Singh et al. 2017).

71
Inulin acts as a dietary fibre providing health benefits, contributes to the decrease of 72 lipid levels, blood glucose and pressure, and laxative action, due to its prebiotic effect

78
Inulin is soluble in water (Yanovsky and Kingsbury 1933), and fractions with a 79 higher degree of polymerization can be precipitated with ethanol (Ku et al. 2003). For 80 this reason, the extraction with hot water and its partial purification utilizing ethanol 81 precipitation has been used as a common method of obtaining commercial inulin from 82 different natural sources (Niness 1999;Álvarez-Borroto et al. 2015). In the mass-83 transfer process of solid-liquid extraction of inulin from its natural plant sources to hot 84 water, however, in addition to the hot water/solid ratio and the water temperature, other 85 factors such as the extraction time, pH, and the agitation of the mixture could exert 86 certain influence (Lingyun et al. 2007;Rubel et al. 2018).

87
The goal of the present work is to determine the optimal conditions that maximize 88 the inulin yield in garlic industrial wastes, through the selection of the best choice of the 89 hot water/weight of garlic waste ratio and temperature, using a central composite design

96
GAIWs were washed and disinfected with a 1% (v/v) ethanol solution before use, 97 then was washed with abundant distilled water, and dried overnight at 80 °C in an oven.

98
Dried GAIWs were chopped with the help of a crusher and a 4 mm of sieve mesh, to 99 obtain a size of the homogeneous particle.

114
To determine the inulin content in the purified extracts, a UV-visible spectrometry.  The response variable (crude (non-purified) inulin yield) was adjusted to a second-135 order statistical model described by the following equation: Where is the yield of crude inulin (g of crude inulin/100 g of GAIW or % (w/w)); 138 0 is the average value of all effects in the model; 11 represents the effect of factor 1 139 (R, mL/g); 21 represents the effect of factor 2 (T, °C); 12 represents the quadratic  Table 1.  The suggested model can be used to find the maximum value of yield based on a 157 combination of R and T, as shown, among others the R 2 , R 2 -adjusted and signal to noise 158 ratio (adequate precision > 4) values (Table 3), and, by the graphs of the normal-plot of 159 residues (Fig. 1A) and in the relationship between predicted vs. actual Y-values (Fig.   160 1B).

FIGURE 1
162 3D-Graph of the crude inulin yield (Y, g/100 g) with the solvent/raw material ratio 164 (R, mL/g) and the temperature (T, °C) shows the existence of an absolute maximum 165 value inside of experimental surface for the yield ( Fig. 2A), which was determined by a 166 numerical algorithm by the Design-Expert software (Fig. 2B).  (Table 4). carried out (Fig. 3).

FIGURE 3
196 By using IR-analysis the main contributions of chemical groups of inulin were 197 determined and summarized (Table 5). The most variable region of the FTIR spectrum among inulin's of different origin is 206 1500 -800 cm -1 (Fig. 3), which is presumably due to the difference between the degrees Not applicable.

239
Availability of data and materials 240 All data obtained or analyzed during this study are included in this article and available 241 from the corresponding author.

242
Ethics approval and consent to participate.

244
Consent for publication 245 The publication of the paper has been agreed by the authors.

247
The authors declare that they have no competing interests.