2.1. Sampling, Milling and Sample Preparation for Analysis

Eight samples of stone milled soft wheat flours (SMF) produced by different mills in Central Italy, plus their corresponding clean grains (Triticum aestivum L.) before milling, were collected at the manufacturer. The grains were a mix of different varieties, coming from different locations and they represented the raw material commonly used by commercial mills.

The same grains obtained from the commercial stone mills were roller milled (see below) in our laboratory to obtain 3 different mill streams, namely refined white flour (RF), coarse bran (CB) and fine bran (FB). The grains were also ground by means of a laboratory disc mill (see below) to produce a whole grain flour (WGF) which was used as reference of a perfect wholemeal flour. So starting from the 8 grain samples, 40 flour samples were obtained.

In addition to the above samples, 7 commercial whole wheat flours from 6 different brands were purchased in stores. Three of them were labelled as stone milled wholemeal, the other 4 as wholemeal only, surely roller milled. These commercial flours (C) were used as comparison.

For roller milling grains were tempered to 15.5–17.5% moisture (for 36–48 h depending on their hardness measured by means of the SKCS 4100 instrument, Perten Instruments, Stockholm, Sweden) and subsequently milled in a Bühler MLU 202 pilot mill (Bühler, Uzwill, Switzerland) equipped with three break rolls, three reduction rolls and six screens, according to method 26-10.02 of the AACCI [12] with an average of 71% extraction rate for the refined flour. Roller milling of wheat produces various fractions with different physicochemical characteristics: F1 (refined flour), F2 (fine bran) and F3 (coarse bran). The germ is found mixed with the bran fractions.

Grains were also ground in a Bühler MLI 204 laboratory disc mill to obtain wholegrain flour (WGF) with ≤0.5 mm particles.

Particle size distribution of flours after stone and roller milling was determined by a mechanical sifter (Bühler MLI 300 B, Bühler, Uzwill, Switzerland) by using 100 g of flour and 5 min sifting time. The sifter was equipped with the following 6 sieves: 38GG (494 µm), 48GG (363 µm), 8xx (183 µm), 10xx (129 µm), 15xx (85 µm), 25PR (35 µm).

Sample preparation before analyses implied that all samples were sifted before analyses and the residue not passing the 494 μm sieve was ground again by the Bühler MLI 204 laboratory mill until it all passed through the sieve.