🍎 Total and reducing sugars and sugar-free extract in fruit and vegetable products — sugars by titration, sugar-free extract by calculation, PN-A-75101-07

Food chemistry PN-A-75101-07

Overview

WHAT THE STANDARD COVERS. The “Scope” field of the PKN catalogue card, in full: “The method consists in reducing, while hot, an alkaline copper salt solution by direct titration with the reducing sugar solution in the presence of methylene blue as indicator. The determination of sugar-free extract consists in establishing the difference between the total extract content and the sum of directly reducing sugars (expressed as invert sugar) and sucrose. The standard contains two annexes with conversion tables”. The titrant is thus the sugar solution from the test sample, and what is titrated is the alkaline copper salt solution; methylene blue shows the end of the titration. The card does not name the method; AB 452 calls it in its scope “Metoda miareczkowa (Lane – Eynona)” (titration method, Lane–Eynon).

STATUS (PKN cards as of 06.11.2026). The card of PN-A-75101-07:1990 (Polish version) has the header “Withdrawn”: publication 25-05-1990, “Withdrawal date: 02-12-2011”, 2 pages, price group A, Food, Agriculture and Forestry Sector, KT 38 Fruit and Vegetable Products, ICS 67.080.01, “Replaces: PN-A-75101:1971 - Polish version”. The card has no “Replaced by”, “Adopts” or “Additional elements” fields — PKN indicates neither a successor, nor an international standard, nor an amendment. That is: it was withdrawn on 02.12.2011 (the same day as sheets 02 and 04 of this series), it was not replaced by anything, and for the result only the status of the reference document changes — the method in the scopes stays the same. We did not search the PKN catalogue for a standard for sugars in juices and products based on the same principle — the PKN search engine returned a server error on the day of reading.

HOW MANY LABORATORIES AND IN WHAT FORM (copy of the accreditation scope database from the production server of 02.11.2026, read on 06.11.2026). All notations of number 75101 with sheet 07 in the reference document field: 11 entries at 7 Polish laboratories (AB 285, AB 313, AB 381, AB 444, AB 452, AB 705, AB 1095); there are no Czech laboratories with this standard in the copy. There are more entries than laboratories because AB 313, AB 444, AB 452 and AB 705 have two each. Notations: “PN-A-75101-07:1990” (AB 313, AB 452, AB 1095 — 5 entries), “PN-90/A-75101/07” (AB 285, AB 444, AB 705 — 5 entries) and “PN-90/A-75101.07” (AB 381). Point 2 of the standard is cited by AB 444 for sugars, point 3 by AB 381, AB 444 and AB 705 for sugar-free extract. No laboratory adds an amendment to this standard. The “Laboratories” tab recognises all these notations and shows the same 7 laboratories and 11 entries (the site’s search query run on the database copy on 06.11.2026). Current PCA scope documents of these 7 laboratories (read on 06.11.2026, issues from 30.10.2025 to 19.10.2026): each of the 11 entries stands in the valid issue with the same range as in the copy; these documents contain no suspension footnote.

WHAT THE LABORATORIES TEST (complete entries from the PCA documents). Sugars — titration method, 3 laboratories: AB 313 — reducing sugars (0,5–60,0) % and total sugars (0,5–85) % in fruit, vegetable and fruit-and-vegetable products, juices, nectars, soft drinks and syrups; AB 444 — total sugars (2,5–80,0) % and reducing sugars (2,5–60,0) % in fruit and vegetable products (point 2); AB 452 — total and reducing sugars “Metoda miareczkowa (Lane – Eynona)”, (1,5–13,0) g/100 ml in fruit and vegetable products and (0,3–13,0) g/100 ml in soft drinks. Calculated quantities (“by calculation”), without range or technique — 5 laboratories: sugar-free extract in fruit and vegetable products (AB 705 — point 3, AB 1095), in fruit, vegetables, products and in juices and nectars (AB 381 — point 3), in percent and in g/l (AB 444 — point 3), in fruit and vegetable juices together with IFU method No. 8 (Rev. 2017) (AB 285); sucrose content in fruit and vegetable products (AB 705).

SUGAR-FREE EXTRACT — WHAT IT IS CALCULATED FROM AND WHO MEASURES THE COMPONENTS. According to the card: sugar-free extract = total extract − (directly reducing sugars expressed as invert sugar + sucrose). No component is measured in the “sugar-free extract” step itself: total extract is a measurement under another standard (in the scopes — PN-A-75101-02, refractometric method), reducing sugars are a measurement under this standard (titration with methylene blue), and the card does not say how the standard establishes sucrose. Who measures the components in the scopes of the same laboratories: total extract — AB 381, AB 444, AB 705 and AB 1095 by the refractometric method according to PN-A-75101-02 (a separate entry in the Knowledge Base), AB 285 — in fruit juices and nectars according to IFU method No. 8 (“by calculation”) and in the flexible scope (“Agricultural products, food”, refractometric method, reference document “Standards”); sugars — according to this standard only AB 444 (point 2); AB 1095 and AB 381 determine sugars in the flexible scope by HPLC-RID (“Food”), AB 705 — in the flexible scope by titration and HPLC-RID, AB 285 — in the flexible scope by titration (this AB 285 entry also lists “sugar-free extract, sucrose by calculation”). A result “sugar-free extract according to PN-A-75101-07” may thus rest on sugars determined by a method other than this standard.

WHERE A SEEMINGLY CORRECT RESULT IS EASY TO GET. First — the components: sugar-free extract is as good as the two results from which it was calculated, and the scope entry “by calculation” does not show by which methods they were obtained; the test report should state them. Second — units: AB 444 calculates sugar-free extract in % and in g/l, AB 452 gives sugars in g/100 ml, AB 313 and AB 444 — in %; components in different units must be brought to one unit before subtracting. Third — range: AB 452 has sugars in the range (1,5–13,0) g/100 ml, while AB 313 and AB 444 go up to 85 % and 80,0 %; these are different units and different upper limits, so a result for a very sweet product (jam, syrup) must be checked against the scope of the laboratory that reports it. Fourth — sucrose: the formula contains the sum of reducing sugars and sucrose; when the product contains sucrose, subtracting reducing sugars alone (without sucrose) understates the sum of sugars and overstates the sugar-free extract. Fifth — the unit of sugars: the card requires reducing sugars to be expressed as invert sugar; a result converted to glucose or another sugar does not fit the formula.

WHAT WE DO NOT GIVE. We did not have the text of the standard — PKN makes it available for a fee. We do not give sample preparation, the way sucrose is determined (e.g. whether by inversion), the concentrations of the copper salt solutions, titration conditions, the conversion tables from the annexes or precision. From the scopes we only know that point 2 of the standard concerns sugars and point 3 sugar-free extract.

Method principle

According to the card of the standard: an alkaline copper salt solution is reduced while hot by titrating it directly with the reducing sugar solution (the solution of the test sample) in the presence of methylene blue as indicator; the result is converted using the tables in the annexes. Sugar-free extract is the difference between the total extract content and the sum of directly reducing sugars (expressed as invert sugar) and sucrose. We DO NOT GIVE the working conditions — we did not have the text of the standard.

Applications

• Fruit and vegetable products (title of the standard); in accreditation scopes also fruit and vegetables, juices, nectars, soft drinks and syrups
• Total sugars and reducing sugars — titration method (at AB 452: Lane–Eynon); 3 laboratories
• Sugar-free extract and sucrose content — calculated quantities (“by calculation”); 5 laboratories
• In accreditation scopes: 7 Polish laboratories, 11 entries

Key parameters

Standard

Standard number

PN-A-75101-07:1990 (Polish version)

Title (PL)

Przetwory owocowe i warzywne — Przygotowanie próbek i metody badań fizykochemicznych — Oznaczanie zawartości cukrów i ekstraktu bezcukrowego

Title (EN)

Fruit and vegetable products — Preparation of samples and methods of physicochemical testing — Determination of sugars and sugar-free extract content

Step-by-step procedure

1. Status of the document

   PKN card: standard withdrawn 02-12-2011, with no successor indicated (card as of 06.11.2026).

2. Sample preparation

   We DO NOT GIVE the preparation of the sample and of the solution for titration — we did not have the text of the standard.

3. Reducing sugars (point 2 according to the scopes)

   The alkaline copper salt solution is titrated while hot with the sugar solution of the test sample in the presence of methylene blue; result from the tables, as invert sugar (from the card).

4. Sucrose

   A component of the sugar-free extract formula; the card does not give how it is determined — WE DO NOT GIVE it.

5. Sugar-free extract (point 3 according to the scopes)

   Total extract (a measurement under another standard, in the scopes PN-A-75101-02) minus the sum of directly reducing sugars (as invert sugar) and sucrose (from the card). In the test report — the methods of both components and the unit.

Required equipment and apparatus

Reagents, media and consumables

Health and safety (OHS)

• TECHNICAL NOTE: sugar-free extract is calculated — the test report states by which methods the total extract and the sugars from which it was calculated were determined
• Titration of a boiling alkaline solution — protect eyes and hands against splashing

Frequently asked questions